Chroma coding mode determination based on matrix-based intra prediction

ABSTRACT

Devices, systems and methods for digital video coding, which includes matrix-based intra prediction methods for video coding, are described. In a representative aspect, a method for video processing includes performing a first determination that a luma video block of a video is coded using a matrix based intra prediction (MIP) mode in which a prediction block of the luma video block is determined by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation, performing, based on the first determination, a second determination about a chroma intra mode to be used for a chroma video block associated with the luma video block, and performing, based on the second determination, a conversion between the chroma video block and a bitstream representation of the chroma video block.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2020/084488, filed on Apr. 13, 2020, which claims the priorityto and benefits of International Patent Application No.PCT/CN2019/082424, filed on Apr. 12, 2019. All the aforementioned patentapplications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to video coding techniques, devices andsystems.

BACKGROUND

In spite of the advances in video compression, digital video stillaccounts for the largest bandwidth use on the internet and other digitalcommunication networks. As the number of connected user devices capableof receiving and displaying video increases, it is expected that thebandwidth demand for digital video usage will continue to grow.

SUMMARY

Devices, systems and methods related to digital video coding, andspecifically, matrix-based intra prediction methods for video coding aredescribed. The described methods may be applied to both the existingvideo coding standards (e.g., High Efficiency Video Coding (HEVC)) andfuture video coding standards (e.g., Versatile Video Coding (VVC)) orcodecs.

A first example video processing method includes generating, for aconversion between a current video block of a video and a codedrepresentation of the current video block, a first most probable mode(MPM) list using a first procedure based on a rule; and performing theconversion between the current video block and the coded representationof the current video block using the first MPM list, where theconversion of the current video block uses a matrix based intraprediction (MIP) mode in which a prediction block of the current videoblock is determined by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, where the rule specifies that the first procedure used forgeneration of the first MPM list is same as a second procedure used forgeneration of a second MPM list for conversion of other video blocks ofthe video that are coded using a non-MIP intra mode that is differentfrom the MIP mode, and where at least a portion of the first MPM list isgenerated based on at least a portion of the second MPM list.

A second example video processing method includes generating, for aconversion between a current video block of a video and a codedrepresentation of the current video block, a most probable mode (MPM)list based on a rule, where the rule is based on whether a neighboringvideo block of the current video block is coded with a matrix basedintra prediction (MIP) mode in which a prediction block of theneighboring video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation; and performing the conversion between the currentvideo block and the coded representation of the current video blockusing the MPM list, where the conversion applies a non-MIP mode to thecurrent video block, and where the non-MIP mode is different from theMIP mode.

A third example video processing method includes decoding a currentvideo block of a video that is coded in a coded representation of thecurrent video block using a matrix based intra prediction (MIP) mode inwhich a prediction block of the current video block is determined byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation; andupdating a line buffer associated with the decoding without storing inthe line buffer information indicating whether the current video blockis coded using the MIP mode.

A fourth example video processing method includes performing aconversion between a current video block and a bitstream representationof the current video block, where the current video block is coded usinga matrix based intra prediction (MIP) mode in which a prediction blockof the current video block is determined by performing, on previouslycoded samples of the video, a boundary downsampling operation, followedby a matrix vector multiplication operation, and selectively followed byan upsampling operation, where a flag is coded in the bitstreampresentation using at most K contexts in an arithmetic coding or adecoding process, where the flag indicates whether the current videoblock is coded using the MIP mode, and where K is greater than or equalto zero.

A fifth example video processing method includes generating, for aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, an intra prediction mode forthe current video block coded with a matrix based intra prediction (MIP)mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation; determining a rule for storing information indicative of theintra prediction mode based on whether the current video block is codedwith the MIP mode; and performing the conversion according to the rule,where the rule defines that a syntax element for the intra predictionmode is stored in the bitstream representation for the current videoblock, and where the rule defines that a mode index for the MIP mode forthe current video block is not stored in the bitstream representation.

A sixth example video processing method includes performing a firstdetermination that a luma video block of a video is coded using a matrixbased intra prediction (MIP) mode in which a prediction block of theluma video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation; performing, based on the first determination, asecond determination about a chroma intra mode to be used for a chromavideo block associated with the luma video block; and performing, basedon the second determination, a conversion between the chroma video blockand a bitstream representation of the chroma video block.

A seventh example video processing method includes performing aconversion between a current video block of a video and a codedrepresentation of the current video block, where the conversion is basedon a determination whether to code the current video block using amatrix based intra prediction (MIP) mode in which a prediction block ofthe current video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation.

An eight example video processing method includes determining, forencoding a current video block of a video into a bitstreamrepresentation of the current video block, according to a rule whetherto use a matrix based intra prediction (MIP) mode and a coding mode thatis different from the MIP mode for encoding the current video block,where the MIP mode includes determining a prediction block of thecurrent video block by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation; and adding, based on the determining, an encodedrepresentation of the current video block to the bitstreamrepresentation.

A ninth example video processing method includes determining that acurrent video block of a video is encoded in a bitstream representationusing a matrix based intra prediction (MIP) mode and a coding mode thatis different from the MIP mode, where the MIP mode includes determininga prediction block of the current video block by performing, onpreviously coded samples of the video, a boundary downsamplingoperation, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation; and generating adecoded representation of the current video block by parsing anddecoding the bitstream representation.

A tenth example video processing method includes making a determinationabout an applicability of a loop filter to a reconstructed block of acurrent video block of a video in a conversion between the video and acoded representation of the current video block, where the current videoblock is coded using a matrix based intra prediction (MIP) mode in whicha prediction block of the current video block is determined byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation; andprocessing the current video block according to the determination.

An eleventh example video processing method includes determining, forencoding a current video block of a video into a bitstreamrepresentation of the current video block, a type of neighboring samplesof the current video block to be used according to a rule; and adding,based on the determining, an encoded representation of the current videoblock to the bitstream representation, where the current video block isencoded using a matrix based intra prediction (MIP) mode in which aprediction block of the current video block is determined by performing,on previously coded samples of the video, a boundary downsamplingoperation, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation.

A twelfth example video processing method includes determining that acurrent video block of a video is encoded in a bitstream representationusing a matrix based intra prediction (MIP) mode and using a type ofneighboring samples of the current video block according to a rule,where the MIP mode includes determining a prediction block of thecurrent video block by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation; and generating a decoded representation of the current videoblock by parsing and decoding the bitstream representation.

A thirteenth example video processing method includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, where the conversion includesgenerating, by using a matrix based intra prediction (MIP) mode, aprediction block for the current video block by selecting and applyingmatrix multiplication using matrices of samples and/or by selecting andadding an offset using offset vectors for the current video block, wherethe samples are obtained from a row and column wise averaging ofpreviously coded samples of the video, and where the selecting is basedon reshaping information associated with applying a luma mapping withchroma scaling (LMCS) technique on a reference picture of the currentvideo block.

A fourteenth example video processing method includes determining that acurrent video block is to be coded using a matrix based intra prediction(MIP) mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation; and performing, based on the determining, a conversionbetween the current video block and a bitstream representation of thecurrent video block, where the performing the conversion is based on arule of co-application of the MIP mode and another coding technique.

A fifteenth example video processing method includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode, where the performing the conversion using the MIPmode includes generating a prediction block by applying matrixmultiplication using matrices of samples obtained from a row and columnwise averaging of previously coded samples of the video, and where thematrices depend on a bit-depth of a sample.

A sixteenth example video processing method includes generating, for acurrent video block of a video, an intermediate prediction signal usinga matrix based intra prediction (MIP) mode in which a prediction blockof the current video block is determined by performing, on previouslycoded samples of the video, a boundary downsampling operation, followedby a matrix vector multiplication operation, and selectively followed byan upsampling operation; generating, based on the intermediateprediction signal, a final prediction signal; and performing, based onthe final prediction signal, a conversion between the current videoblock and a bitstream representation of the current video block.

A seventeenth example video processing method includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode, where the performing the conversion includesusing an interpolation filter in an upsampling process for the MIP mode,where, in the MIP mode, a matrix multiplication is applied to a firstset of samples obtained from a row and column wise averaging ofpreviously coded samples of the video, and the interpolation filter isapplied to a second set of samples obtained from the matrixmultiplication, and where interpolation filter excludes a bilinearinterpolation filter.

An eighteenth example video processing method includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block according to a rule, where therule specifies a relationship between applicability of a matrix basedintra prediction (MIP) mode or a transform mode during the conversion,where the MIP mode includes determining a prediction block of thecurrent video block by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, and where the transform mode specifies use of a transformoperation for the determining the prediction block for the current videoblock.

A nineteenth example video processing method includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode in which a prediction block of the current videoblock is determined by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, where the performing the conversion includes deriving,according to a rule, boundary samples by applying a left bit shiftoperation or a right bit shift operation on a sum of at least onereference boundary sample, and where the rule determines whether toapply the left bit shift operation or the right bit shift operation.

A twentieth example video processing method includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode in which a prediction block of the current videoblock is determined by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, where the prediction samples predSamples[xHor+dX][yHor] aredetermined according to following formula in the upsampling operation:predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor,andpredSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer,where offsetHor and offsetVer are integers, where upHor is a function ofthe current video block width and a pre-defined value based on thecurrent video block size, where upVer is a function of the current videoblock height and the pre-defined value based on the current video blocksize; where dX is 1 . . . upHor−1, where dY is 1 . . . upVer−1, andwhere xHor are positions based on the upHor and yHor are positions basedon the upVer.

A twenty-first example video processing method includes generating, fora conversion between a current video block of a video and a bitstreamrepresentation of the current video block, an intra prediction mode forthe current video block coded with a matrix based intra prediction (MIP)mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation; determining a rule for storing information indicative of theintra prediction mode based on whether the current video block is codedwith the MIP mode; and performing the conversion according to the rule,where the rule defines that the bitstream representation excludes astorage of information indicative of the MIP mode associated with thecurrent video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using an affinelinear weighted intra prediction (ALWIP) mode, constructing, based onthe determining, at least a portion of a most probable mode (MPM) listfor the ALWIP mode based on an at least a portion of an MPM list for anon-ALWIP intra mode, and performing, based on the MPM list for theALWIP mode, a conversion between the current video block and a bitstreamrepresentation of the current video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a luma component of a current video block iscoded using an affine linear weighted intra prediction (ALWIP) mode,inferring, based on the determining, a chroma intra mode, andperforming, based on the chroma intra mode, a conversion between thecurrent video block and a bitstream representation of the current videoblock.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using an affinelinear weighted intra prediction (ALWIP) mode, and performing, based onthe determining, a conversion between the current video block and abitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using a codingmode different from an affine linear weighted intra prediction (ALWIP)mode, and performing, based on the determining, a conversion between thecurrent video block and a bitstream representation of the current videoblock.

In yet another representative aspect, the above-described method isembodied in the form of processor-executable code and stored in acomputer-readable program medium.

In yet another representative aspect, a device that is configured oroperable to perform the above-described method is disclosed. The devicemay include a processor that is programmed to implement this method.

In yet another representative aspect, a video decoder apparatus mayimplement a method as described herein.

The above and other aspects and features of the disclosed technology aredescribed in greater detail in the drawings, the description and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of 33 intra prediction directions.

FIG. 2 shows an example of 67 intra prediction modes.

FIG. 3 shows an example of locations of samples used for the derivationof the weights of the linear model.

FIG. 4 shows an example of four reference lines neighboring a predictionblock.

FIG. 5A and FIG. 5B show examples of sub-partitions depending on blocksize.

FIG. 6 shows an example of ALWIP for 4×4 blocks.

FIG. 7 shows an example of ALWIP for 8×8 blocks.

FIG. 8 shows an example of ALWIP for 8×4 blocks.

FIG. 9 shows an example of ALWIP for 16×16 blocks.

FIG. 10 shows an example of neighboring blocks using in MPM listconstruction.

FIG. 11 shows a flowchart of an example method for matrix-based intraprediction, in accordance with the disclosed technology.

FIG. 12 shows a flowchart of another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 13 shows a flowchart of yet another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 14 shows a flowchart of yet another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 15 is a block diagram of an example of a hardware platform forimplementing a visual media decoding or a visual media encodingtechnique described in the present document.

FIG. 16 is a block diagram showing an example video processing system inwhich various techniques disclosed herein may be implemented.

FIG. 17 is a block diagram that illustrates an example video codingsystem that may utilize the techniques of this disclosure.

FIG. 18 is a block diagram illustrating an example of video encoder.

FIG. 19 is a block diagram illustrating an example of video decoder.

FIGS. 20-38 show example flowcharts of additional example methods formatrix-based intra prediction, in accordance with the disclosedtechnology.

DETAILED DESCRIPTION

Due to the increasing demand of higher resolution video, video codingmethods and techniques are ubiquitous in modern technology. Video codecstypically include an electronic circuit or software that compresses ordecompresses digital video and are continually being improved to providehigher coding efficiency. A video codec converts uncompressed video to acompressed format or vice versa. There are complex relationships betweenthe video quality, the amount of data used to represent the video(determined by the bit rate), the complexity of the encoding anddecoding algorithms, sensitivity to data losses and errors, ease ofediting, random access, and end-to-end delay (latency). The compressedformat usually conforms to a standard video compression specification,e.g., the High Efficiency Video Coding (HEVC) standard (also known asH.265 or MPEG-H Part 2), the Versatile Video Coding (VVC) standard to befinalized, or other current and/or future video coding standards.

Embodiments of the disclosed technology may be applied to existing videocoding standards (e.g., HEVC, H.265) and future standards to improveruntime performance. Section headings are used in the present documentto improve readability of the description and do not in any way limitthe discussion or the embodiments (and/or implementations) to therespective sections only.

1 A Brief Review on HEVC 1.1 Intra Prediction in HEVC/H.265

Intra prediction involves producing samples for a given TB (transformblock) using samples previously reconstructed in the considered colorchannel. The intra prediction mode is separately signaled for the lumaand chroma channels, with the chroma channel intra prediction modeoptionally dependent on the luma channel intra prediction mode via the‘DM_CHROMA’ mode. Although the intra prediction mode is signaled at thePB (prediction block) level, the intra prediction process is applied atthe TB level, in accordance with the residual quad-tree hierarchy forthe CU, thereby allowing the coding of one TB to have an effect on thecoding of the next TB within the CU, and therefore reducing the distanceto the samples used as reference values.

HEVC includes 35 intra prediction modes—a DC mode, a planar mode and 33directional, or ‘angular’ intra prediction modes. The 33 angular intraprediction modes are illustrated in FIG. 1.

For PBs associated with chroma color channels, the intra prediction modeis specified as either planar, DC, horizontal, vertical, ‘DM_CHROMA’mode or sometimes diagonal mode ‘34’.

Note for chroma formats 4:2:2 and 4:2:0, the chroma PB may overlap twoor four (respectively) luma PBs; in this case the luma direction forDM_CHROMA is taken from the top left of these luma PBs.

The DM_CHROMA mode indicates that the intra prediction mode of the lumacolor channel PB is applied to the chroma color channel PBs. Since thisis relatively common, the most-probable-mode coding scheme of theintra_chroma_pred_mode is biased in favor of this mode being selected.

2 Examples of Intra Prediction in VVC 2.1 Intra Mode Coding with 67Intra Prediction Modes

To capture the arbitrary edge directions presented in natural video, thenumber of directional intra modes is extended from 33, as used in HEVC,to 65. The additional directional modes are depicted as red dottedarrows in FIG. 2, and the planar and DC modes remain the same. Thesedenser directional intra prediction modes apply for all block sizes andfor both luma and chroma intra predictions.

2.2 Examples of the Cross-Component Linear Model (CCLM)

In some embodiments, and to reduce the cross-component redundancy, across-component linear model (CCLM) prediction mode (also referred to asLM), is used in the JEM, for which the chroma samples are predictedbased on the reconstructed luma samples of the same CU by using a linearmodel as follows:pred_(c)(i,j)=β·rec_(L)′(i,j)+β  (1)

Here, pred_(c) (i,j) represents the predicted chroma samples in a CU andrec_(L)′(i,j) represents the downsampled reconstructed luma samples ofthe same CU. Linear model parameter α and β are derived from therelation between luma values and chroma values from two samples, whichare luma sample with minimum sample value and with maximum sample insidethe set of downsampled neighboring luma samples, and their correspondingchroma samples. FIG. 3 shows an example of the location of the left andabove samples and the sample of the current block involved in the CCLMmode.

This parameter computation is performed as part of the decoding process,and is not just as an encoder search operation. As a result, no syntaxis used to convey the α and β values to the decoder.

For chroma intra mode coding, a total of 8 intra modes are allowed forchroma intra mode coding. Those modes include five traditional intramodes and three cross-component linear model modes (CCLM, LM_A, andLM_L). Chroma mode coding directly depends on the intra prediction modeof the corresponding luma block. Since separate block partitioningstructure for luma and chroma components is enabled in I slices, onechroma block may correspond to multiple luma blocks. Therefore, forChroma DM mode, the intra prediction mode of the corresponding lumablock covering the center position of the current chroma block isdirectly inherited.

2.3 Multiple Reference Line (MRL) Intra Prediction

Multiple reference line (MRL) intra prediction uses more reference linesfor intra prediction. In FIG. 4, an example of 4 reference lines isdepicted, where the samples of segments A and F are not fetched fromreconstructed neighboring samples but padded with the closest samplesfrom Segment B and E, respectively. HEVC intra-picture prediction usesthe nearest reference line (i.e., reference line 0). In MRL, 2additional lines (reference line 1 and reference line 3) are used. Theindex of selected reference line (mrl_idx) is signalled and used togenerate intra predictor. For reference line idx, which is greater than0, only include additional reference line modes in MPM list and onlysignal mpm index without remaining mode.

2.4 Intra Sub-Partitions (ISP)

The Intra Sub-Partitions (ISP) tool divides luma intra-predicted blocksvertically or horizontally into 2 or 4 sub-partitions depending on theblock size. For example, minimum block size for ISP is 4×8 (or 8×4). Ifblock size is greater than 4×8 (or 8×4) then the corresponding block isdivided by 4 sub-partitions. FIG. 5 shows examples of the twopossibilities. All sub-partitions fulfill the condition of having atleast 16 samples.

For each sub-partition, reconstructed samples are obtained by adding theresidual signal to the prediction signal. Here, a residual signal isgenerated by the processes such as entropy decoding, inversequantization and inverse transform. Therefore, the reconstructed samplevalues of each sub-partition are available to generate the prediction ofthe next sub-partition, and each sub-partition is processed repeatedly.In addition, the first sub-partition to be processed is the onecontaining the top-left sample of the CU and then continuing downwards(horizontal split) or rightwards (vertical split). As a result,reference samples used to generate the sub-partitions prediction signalsare only located at the left and above sides of the lines. Allsub-partitions share the same intra mode.

2.5 Affine Linear Weighted Intra Prediction (ALWIP or Matrix-Based IntraPrediction)

Affine linear weighted intra prediction (ALWIP, a.k.a. Matrix basedintra prediction (MIP)) is proposed in JVET-N0217.

In JVET-N0217, two tests are conducted. In test 1, ALWIP is designedwith a memory restriction of 8K bytes and at most 4 multiplications persample. Test 2 is similar to test 1, but further simplifies the designin terms of memory requirement and model architecture.

-   -   Single set of matrices and offset vectors for all block shapes.    -   Reduction of number of modes to 19 for all block shapes.    -   Reduction of memory requirement to 576010-bit values, that is        7.20 Kilobyte.    -   Linear interpolation of predicted samples is carried out in a        single step per direction replacing iterative interpolation as        in the first test.

2.5.1 Test 1 of JVET-N0217

For predicting the samples of a rectangular block of width W and heightH, affine linear weighted intra prediction (ALWIP) takes one line of Hreconstructed neighboring boundary samples left of the block and oneline of W reconstructed neighboring boundary samples above the block asinput. If the reconstructed samples are unavailable, they are generatedas it is done in the conventional intra prediction.

The generation of the prediction signal is based on the following threesteps:

Out of the boundary samples, four samples in the case of W=H=4 and eightsamples in all other cases are extracted by averaging.

A matrix vector multiplication, followed by addition of an offset, iscarried out with the averaged samples as an input. The result is areduced prediction signal on a subsampled set of samples in the originalblock.

The prediction signal at the remaining positions is generated from theprediction signal on the subsampled set by linear interpolation which isa single step linear interpolation in each direction.

The matrices and offset vectors needed to generate the prediction signalare taken from three sets S₀, S₁, S₂ of matrices. The set S₀ consists of18 matrices A₀ ^(i), i ∈{0, . . . , 17} each of which has 16 rows and 4columns and 18 offset vectors b₀ ^(i), i ∈{0, . . . , 17} each of size16. Matrices and offset vectors of that set are used for blocks of size4×4. The set S₁ consists of 10 matrices A₁ ^(i), i ∈{0, . . . , 9}, eachof which has 16 rows and 8 columns and 10 offset vectors bf, i ∈{0, . .. , 9} each of size 16. Matrices and offset vectors of that set are usedfor blocks of sizes 4×8, 8×4 and 8×8. Finally, the set S₂ consists of 6matrices A₂ ^(i), i ∈{0, . . . , 5}, each of which has 64 rows and 8columns and of 6 offset vectors b₂ ^(i), i ∈{0, . . . , 5} of size 64.Matrices and offset vectors of that set or parts of these matrices andoffset vectors are used for all other block-shapes.

The total number of multiplications needed in the computation of thematrix vector product is always smaller than or equal to 4×W×H. In otherwords, at most four multiplications per sample are required for theALWIP modes.

2.5.2 Averaging of the Boundary

In a first step, the input boundaries bdry^(top) and bdry^(left) arereduced to smaller boundaries bdry_(red) ^(top) and bdry_(red) ^(left).Here, bdry_(red) ^(top) and bdry_(red) ^(left) both consists of 2samples in the case of a 4×4-block and both consist of 4 samples in allother cases.

In the case of a 4×4-block, for 0≤i<2, one defines

${bdr{y_{red}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{1}{bdr{y^{top}\left\lbrack {{i \cdot 2} + j} \right\rbrack}}} \right) + 1} \right) ⪢ 1}$

and defines bdry_(red) ^(left) analogously.

Otherwise, if the block-width W is given as W=4·2^(k), for 0≤i<4, onedefines

${{bdr}{y_{red}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{2^{k} - 1}{bdr{y^{top}\left\lbrack {{i \cdot 2^{k}} + j} \right\rbrack}}} \right) + \left( {1 ⪡ \left( {k - 1} \right)} \right)} \right) ⪢ k}$

and defines bdry_(red) ^(left) analogously.

The two reduced boundaries bdry_(red) ^(top) and bdry_(red) ^(left) areconcatenated to a reduced boundary vector bdry_(red) which is thus ofsize four for blocks of shape 4×4 and of size eight for blocks of allother shapes. If mode refers to the ALWIP-mode, this concatenation isdefined as follows:

${bdry_{red}} = \left\{ {\begin{matrix}\left\lbrack {{{bdr}y_{red}^{top}}\ ,\ {{bdr}y_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} < 18}}} \\\left\lbrack {{bdry_{red}^{left}},\ {{bdr}y_{red}^{top}}} \right\rbrack & {{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 18}}} \\\left\lbrack {{{bdr}y_{red}^{top}}\ ,\ {{bdr}y_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} < 10}} \\\left\lbrack {{{bdr}y_{red}^{left}},\ {{bdr}y_{red}^{top}}} \right\rbrack & {{{for}{\mspace{11mu}\ }{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 10}} \\\left\lbrack {{{bdr}y_{red}^{top}}\ ,\ {{bdr}y_{red}^{left}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} < 6} \\\left\lbrack {{{bdr}y_{red}^{left}},\ {{bdr}y_{red}^{top}}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 6}\end{matrix}.} \right.$

Finally, for the interpolation of the subsampled prediction signal, onlarge blocks a second version of the averaged boundary is needed.Namely, if min(W,H)>8 and W≥H, one writes W=8*2^(l), and, for 0≤i<8,defines

${{bdr}{y_{redII}^{top}\lbrack i\rbrack}} = {\left( {\left( {\sum\limits_{j = 0}^{2^{l} - 1}{bdr{y^{top}\left\lbrack {{i \cdot 2^{l}} + j} \right\rbrack}}} \right) + \left( {1 ⪡ \left( {l - 1} \right)} \right)} \right) ⪢ {l.}}$

If min(W,H)>8 and H>W, one defines bdry_(redII) ^(left) analogously.

2.5.3 Generation of the Reduced Prediction Signal by Matrix VectorMultiplication

Out of the reduced input vector bdry_(red) one generates a reducedprediction signal pred_(red). The latter signal is a signal on thedownsampled block of width W_(red) and height H_(red). Here, W_(red) andH_(red) are defined as:

$W_{red} = \left\{ {{\begin{matrix}4 & {{{{for}\mspace{14mu}\max\left( {W,H} \right)} \leq 8}\mspace{14mu}} \\{\min\left( {W,8} \right)} & {{{for}\mspace{14mu}\max\left( {W,H} \right)} > 8}\end{matrix}H_{red}} = \left\{ \begin{matrix}4 & {{{{for}\mspace{14mu}\max\left( {W,H} \right)} \leq 8}\mspace{14mu}} \\{\min\left( {H,8} \right)} & {{{for}\mspace{14mu}\max\left( {W,H} \right)} > 8}\end{matrix} \right.} \right.$

The reduced prediction signal pred_(red) is computed by calculating amatrix vector product and adding an offset:pred_(red) =A·bdry_(red) +b

Here, A is a matrix that has W_(red)·H_(red) rows and 4 columns if W=H=4and 8 columns in all other cases. b is a vector of size W_(red)·H_(red).

The matrix A and the vector b are taken from one of the sets S₀, S₁, S₂as follows. One defines an index idx=idx(W,H) as follows:

${id{x\left( {W,H} \right)}} = \left\{ \begin{matrix}0 & {{{for}\mspace{14mu} W} = {H = 4}} \\1 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = 8} \\2 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8.}\end{matrix} \right.$

Moreover, one puts m as follows:

$m = \left\{ \begin{matrix}{mode} & {{{for}\ W} = {H = {{4\mspace{14mu}{and}\ {mode}} < 18}}} \\{{mode} - 17} & {{{for}\ W} = {H = {{4\mspace{14mu}{and}\ {mode}} \geq 18}}} \\{mode} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\ {mode}} < 10}} \\{{mode} - 9} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\ {mode}} \geq 10}} \\{mode} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\ {mode}} < 6} \\{{mode} - 5} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\ {mode}} \geq 6.}\end{matrix} \right.$

Then, if idx≤1 or idx=2 and min(W,H)>4, one puts A=A_(idx) ^(m) andb=b_(idx) ^(m). In the case that idx=2 and min(W,H)=4, one lets A be thematrix that arises by leaving out every row of A_(idx) ^(m) that, in thecase W=4, corresponds to an odd x-coordinate in the downsampled block,or, in the case H=4, corresponds to an odd y-coordinate in thedownsampled block.

Finally, the reduced prediction signal is replaced by its transpose inthe following cases:

-   -   W=H=4 and mode≥18    -   max(W,H)=8 and mode≥10    -   max(W,H)>8 and mode≥6

The number of multiplications required for calculation of pred_(red) is4 in the case of W=H=4 since in this case A has 4 columns and 16 rows.In all other cases, A has 8 columns and W_(red)·H_(red) rows and oneimmediately verifies that in these cases 8·W_(red)·H_(red)≤4·W·Hmultiplications are required, i.e. also in these cases, at most 4multiplications per sample are needed to compute pred_(red).

2.5.4 Illustration of the Entire ALWIP Process

The entire process of averaging, matrix vector multiplication and linearinterpolation is illustrated for different shapes in FIGS. 6-9. Note,that the remaining shapes are treated as in one of the depicted cases.

1. Given a 4×4 block, ALWIP takes two averages along each axis of theboundary. The resulting four input samples enter the matrix vectormultiplication. The matrices are taken from the set S₀. After adding anoffset, this yields the 16 final prediction samples. Linearinterpolation is not necessary for generating the prediction signal.Thus, a total of (4·16)/(4·4)=4 multiplications per sample areperformed.

2. Given an 8×8 block, ALWIP takes four averages along each axis of theboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₁. This yields 16samples on the odd positions of the prediction block. Thus, a total of(8·16)/(8·8)=2 multiplications per sample are performed. After adding anoffset, these samples are interpolated vertically by using the reducedtop boundary. Horizontal interpolation follows by using the originalleft boundary.

3. Given an 8×4 block, ALWIP takes four averages along the horizontalaxis of the boundary and the four original boundary values on the leftboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₁. This yields 16samples on the odd horizontal and each vertical positions of theprediction block. Thus, a total of (8·16)/(8·4)=4 multiplications persample are performed. After adding an offset, these samples areinterpolated horizontally by using the original left boundary.

4. Given a 16×16 block, ALWIP takes four averages along each axis of theboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₂. This yields 64samples on the odd positions of the prediction block. Thus, a total of(8·64)/(16·16)=2 multiplications per sample are performed. After addingan offset, these samples are interpolated vertically by using eightaverages of the top boundary. Horizontal interpolation follows by usingthe original left boundary. The interpolation process, in this case,does not add any multiplications. Therefore, totally, twomultiplications per sample are required to calculate ALWIP prediction.

For larger shapes, the procedure is essentially the same and it is easyto check that the number of multiplications per sample is less thanfour.

For W×8 blocks with W>8, only horizontal interpolation is necessary asthe samples are given at the odd horizontal and each vertical positions.

Finally, for W×4 blocks with W>8, let A_kbe the matrix that arises byleaving out every row that corresponds to an odd entry along thehorizontal axis of the downsampled block. Thus, the output size is 32and again, only horizontal interpolation remains to be performed.

The transposed cases are treated accordingly.

2.5.5 Single Step Linear Interpolation

For a W×H block with max(W,H)≥8, the prediction signal arises from thereduced prediction signal pred_(red) on W_(red)×H_(red) by linearinterpolation. Depending on the block shape, linear interpolation isdone in vertical, horizontal or both directions. If linear interpolationis to be applied in both directions, it is first applied in horizontaldirection if W<H and it is first applied in vertical direction, else.

Consider without loss of generality a W×H block with max(W,H)≥8 and W≥H.Then, the one-dimensional linear interpolation is performed as follows.Without loss of generality, it suffices to describe linear interpolationin vertical direction. First, the reduced prediction signal is extendedto the top by the boundary signal. Define the vertical upsampling factorU_(ver)=H/H_(red) and write U_(ver)=2^(u) ^(ver) >1. Then, define theextended reduced prediction signal by

${pre{{d_{red}\lbrack x\rbrack}\left\lbrack {- 1} \right\rbrack}} = \left\{ {\begin{matrix}{{{bdr}{y_{red}^{top}\lbrack x\rbrack}}\mspace{11mu}} & {{{for}\mspace{14mu} W} = 8} \\{{{bdr}{y_{redII}^{top}\lbrack x\rbrack}}\mspace{11mu}} & {{{for}\mspace{14mu} W} > 8}\end{matrix}.} \right.$

Then, from this extended reduced prediction signal, the verticallylinear interpolated prediction signal is generated by

${pre{{d_{red}^{{ups},{ver}}\lbrack x\rbrack}\left\lbrack {{U_{ver} \cdot y} + k} \right\rbrack}} = {\left( {{\left( {U_{ver} - k - 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\left\lbrack {y - 1} \right\rbrack}} + {\left( {k + 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\lbrack y\rbrack}} + \frac{U_{ver}}{2}} \right) ⪢ u_{ver}}$  for  0 ≤ x < W_(red), 0 ≤ y < H_(red)  and  0 ≤ k < U_(ver).2.5.6 Signalization of the Proposed Intra Prediction Modes

For each Coding Unit (CU) in intra mode, a flag indicating if an ALWIPmode is to be applied on the corresponding Prediction Unit (PU) or notis sent in the bitstream. The signalization of the latter index isharmonized with MRL in the same way as in JVET-M0043. If an ALWIP modeis to be applied, the index predmode of the ALWIP mode is signaled usinga MPM-list with 3 MPMS.

Here, the derivation of the MPMs is performed using the intra-modes ofthe above and the left PU as follows. There are three fixed tablesmap_angular_to_alwip_(idx), idx ∈{0, 1, 2} that assign to eachconventional intra prediction mode predmode_(Angular) an ALWIP modepredmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an indexidx(PU)=idx(W,H)∈{0,1,2}

that indicates from which of the three sets the ALWIP-parameters are tobe taken as in Section 2.5.3.

If the above Prediction Unit PU_(above) is available, belongs to thesame CTU as the current PU and is in intra mode, ifidx(PU)=idx(PU_(above)) and if ALWIP is applied on PU_(above) withALWIP-mode predmode_(ALWIP) ^(above), one putsmode_(ALWIP) ^(above)=predmode^(above) _(ALWIP).

If the above PU is available, belongs to the same CTU as the current PUand is in intra mode and if a conventional intra prediction modepredmode_(Angular) ^(above) is applied on the above PU, one putsmode_(ALWIP) ^(above)=map_angular_to_alwip_(idx(PU) _(above)₎[predmode_(Angular) ^(above)].

In all other cases, one putsmode_(ALWIP) ^(above)=−1,

which means that this mode is unavailable. In the same way but withoutthe restriction that the left PU needs to belong to the same CTU as thecurrent PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx ∈{0, 1, 2} areprovided, each of which contains three distinct ALWIP modes. Out of thedefault list list_(idx(PU)) and the modes mode_(ALWIP) ^(above) andmode_(ALWIP) ^(left), one constructs three distinct MPMs by substituting−1 by default values as well as eliminating repetitions.

The left neighboring block and above neighboring block used in the ALWIPMPM list construction is A1 and B1 as shown in FIG. 10.

2.5.7 Adapted MPM-List Derivation for Conventional Luma and ChromaIntra-Prediction Modes

The proposed ALWIP-modes are harmonized with the MPM-based coding of theconventional intra-prediction modes as follows. The luma and chromaMPM-list derivation processes for the conventional intra-predictionmodes uses fixed tables map_alwip_to_angular_(idx), idx ∈{0, 1, 2},mapping an ALWIP-mode predmode_(ALWIP) on a given PU to one of theconventional intra-prediction modespredmode_(Angular)=map_alwip_to_angular_(idx(PU))[predmode_(ALWIP)]

For the luma MPM-list derivation, whenever a neighboring luma block isencountered which uses an ALWIP-mode predmode_(ALWIP), this block istreated as if it was using the conventional intra-prediction modepredmode_(Angular). For the chroma MPM-list derivation, whenever thecurrent luma block uses an LWIP-mode, the same mapping is used totranslate the ALWIP-mode to a conventional intra prediction mode.

2.5.8 Corresponding Modified Working Draft

In some embodiments, as described in this section, portions related tointra_lwip_flag, intra_lwip_mpm_flag, intra_lwip_mpm_idx andintra_lwip_mpm_remainder have been added to the working draft based onembodiments of the disclosed technology.

In some embodiments, as described in this section, the <begin> and <end>tags are used to denote additions and modifications to the working draftbased on embodiments of the disclosed technology.

Syntax Tables Coding Unit Syntax

Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {  if(tile_group_type !=I | | sps_ibc_enabled_flag ) {   if( treeType !=DUAL_TREE_CHROMA )    cu_skip_flag[x0][y0] ae(v)   if(cu_skip_flag[x0][y0] = = 0 && tile_group_type != I )    pred_mode_flagae(v)   if( ( ( tile_group_type = = I && cu_skip_flag[x0][y0] = =0 ) | |   ( tile_group_type != I && CuPredMode[x0][y0] != MODE_INTRA ) ) &&   sps_ibc_enabled_flag )    pred_mode_ibc_flag ae(v)  }  if(CuPredMode[x0][y0] = = MODE_INTRA ) {   if( sps_pcm_enabled_flag &&   cbWidth >= MinIpcmCbSizeY && cbWidth <= MaxIpcmCbSizeY &&   cbHeight >= MinIpcmCbSizeY && cbHeight <= MaxIpcmCbSizeY )   pcm_flag[x0][y0] ae(v)   if( pcm_flag[x0][y0] ) {    while(!byte_aligned( ) )     pcm_alignment_zero_bit f(1)    pcm_sample(cbWidth, cbHeight, treeType)   } else {    if( treeType = = SINGLE_TREE| | treeType = = DUAL_TREE_LUMA ) {     if( Abs( Log2( cbWidth ) − Log2(cbHeight ) ) <= 2 )      intra_lwip_flag[x0][y0] ae(v)     if(intra_lwip_flag[x0][y0] ) {       intra_lwip_mpm_flag[x0][y0] ae(v)     if( intra_lwip_mpm_flag[x0][y0] )       intra_lwip_mpm_idx[x0][y0]ae(v)      else       intra_lwip_mpm_remainder[x0][y0] ae(v)     } else{      if( ( y0 % CtbSizeY ) > 0 )       intra_luma_ref_idx[x0][y0]ae(v)      if (intra_luma_ref_idx[x0][y0] = = 0 &&       ( cbWidth <=MaxTbSizeY | | cbHeight <= MaxTbSizeY ) &&       ( cbWidth * cbHeight >MinTbSizeY * MinTbSizeY ))       intra_subpartitions_mode_flag[x0][y0]ae(v)      if( intra_subpartitions_mode_flag[x0][y0] = = 1 &&      cbWidth <= MaxTbSizeY && cbHeight <= MaxTbSizeY )      intra_subpartitions_split_flag[x0][y0] ae(v)      if(intra_luma_ref_idx[x0][y0] = = 0 &&      intra_subpartitions_mode_flag[x0][y0] = = 0 )      intra_luma_mpm_flag[x0][y0] ae(v)      if(intra_luma_mpm_flag[x0][y0] )        intra_luma_mpm_idx[x0][y0] ae(v)     else       intra_luma_mpm_remainder[x0][y0] ae(v)    }   }   if(treeType = = SINGLE_TREE | | treeType = = DUAL_TREE_CHROMA )   intra_chroma_pred_mode[x0][y0] ae(v)   }  } else if( treeType !=DUAL_TREE_CHROMA ) { /* MODE_INTER or MODE_IBC */   ...

Semantics

<begin>intra_lwip_flag[x0][y0] equal to 1 specifies that the intraprediction type for luma samples is affine linear weighted intraprediction. intra_lwip_flag[x0][y0] equal to 0 specifies that the intraprediction type for luma samples is not affine linear weighted intraprediction.When intra_lwip_flag[x0][y0] is not present, it is inferred to be equalto 0.The syntax elements intra_lwip_mpm_flag[x0][y0],intra_lwip_mpm_idx[x0][y0] and intra_lwip_mpm_remainder [x0][y0] specifythe affine linear weighted intra prediction mode for luma samples. Thearray indices x0, y0 specify the location (x0, y0) of the top-left lumasample of the considered coding block relative to the top-left lumasample of the picture. When intra_lwip_mpm_flag[x0][y0] is equal to 1,the affine linear weighted intra prediction mode is inferred from aneighboring intra-predicted coding unit according to clause 8.4.X.

When intra_lwip_mpm_flag[x0][y0] is not present, it is inferred to beequal to 1.<end>

intra_subpartitions_split_flag[x0][y0] specifies whether the intrasubpartitions split type is horizontal or vertical. Whenintra_subpartitions_split_flag[x0][y0] is not present, it is inferred asfollows:

-   -   If intra_lwip_flag[x0][y0] is equal to 1,        intra_subpartitions_split_flag[x0][y0] is inferred to be equal        to 0.    -   Otherwise, the following applies:        -   If cbHeight is greater than MaxTbSizeY,            intra_subpartitions_split_flag[x0][y0] is inferred to be            equal to 0.        -   Otherwise (cbWidth is greater than MaxTbSizeY),            intra_subpartitions_split_flag[x0][y0] is inferred to be            equal to 1.

Decoding Process 8.4.1 General Decoding Process for Coding Units Codedin Intra Prediction Mode

Inputs to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current coding block relative to the top-left luma sample of the        current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples,    -   a variable treeType specifying whether a single or a dual tree        is used and if a dual tree is used, it specifies whether the        current tree corresponds to the luma or chroma components.        Output of this process is a modified reconstructed picture        before in-loop filtering.        The derivation process for quantization parameters as specified        in clause 8.7.1 is invoked with the luma location (xCb, yCb),        the width of the current coding block in luma samples cbWidth        and the height of the current coding block in luma samples        cbHeight, and the variable treeType as inputs.        When treeType is equal to SINGLE_TREE or treeType is equal to        DUAL_TREE_LUMA, the decoding process for luma samples is        specified as follows:    -   If pcm_flag[xCb][yCb] is equal to 1, the reconstructed picture        is modified as follows:        S        _(L)[xCb+i][yCb+j]=pcm_sample_luma[(cbHeight*j)+i]<<(BitDepth_(γ)−PcmBitDepth_(γ)),  (8-6)    -   with i=0 . . . cbWidth−1, j=0 . . . cbHeight−1    -   Otherwise, the following applies:    -   1. The luma intra prediction mode is derived as follows:        -   If intra_lwip_flag[xCb][yCb] is equal to 1, the derivation            process for the affine linear weighted intra prediction mode            as specified in clause 8.4.X is invoked with the luma            location (xCb, yCb), the width of the current coding block            in luma samples cbWidth and the height of the current coding            block in luma samples cbHeight as input.        -   Otherwise, the derivation process for the luma intra            prediction mode as specified in clause 8.4.2 is invoked with            the luma location (xCb, yCb), the width of the current            coding block in luma samples cbWidth and the height of the            current coding block in luma samples cbHeight as input.    -   2. The general decoding process for intra blocks as specified in        clause 8.4.4.1 is invoked with the luma location (xCb, yCb), the        tree type treeType, the variable nTbW set equal to cbWidth, the        variable nTbH set equal to cbHeight, the variable predModeIntra        set equal to IntraPredModeY[xCb][yCb], and the variable cldx set        equal to 0 as inputs, and the output is a modified reconstructed        picture before in-loop filtering.        <begin>

8.4.X Derivation Process for Affine Linear Weighted Intra PredictionMode

Input to this Process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        In this process, the affine linear weighted intra prediction        mode IntraPredModeY[xCb][yCb] is derived.        IntraPredModeY[xCb][yCb] is derived by the following ordered        steps:    -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb) and (xCb, yCb−1), respectively.    -   2. For X being replaced by either A or B, the variables        candLwipModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause 6.4.X [Ed. (BB): Neighboring blocks availability            checking process tbd] is invoked with the location (xCurr,            yCurr) set equal to (xCb, yCb) and the neighboring location            (xNbY, yNbY) set equal to (xNbX, yNbX) as inputs, and the            output is assigned to availableX.        -   The candidate affine linear weighted intra prediction mode            candLwipModeX is derived as follows:            -   If one or more of the following conditions are true,                candLwipModeX is set equal to −1.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                    and mh_intra_flag[xNbX][yNbX] is not equal to 1.                -   pcm_flag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than ((yCb>>Ctb                    Log 2SizeY)<<Ctb Log 2SizeY).            -   Otherwise, the following applies:                -   The size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the current coding block in luma samples                    cbWidth and the height of the current coding block                    in luma samples cbHeight as input, and the output is                    assigned to variable sizeId.                -   If intra_lwip_flag[xNbX][yNbX] is equal to 1, the                    size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the neighboring coding block in luma                    samples nbWidthX and the height of the neighboring                    coding block in luma samples nbHeightX as input, and                    the output is assigned to variable sizeIdX.                -    If sizeId is equal to sizeIdX, candLwipModeX is set                    equal to IntraPredModeY[xNbX][yNbX].                -    Otherwise, candLwipModeX is set equal to −1.                -   Otherwise, candLwipModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X1.    -   3. The candLwipModeList[x] with x=0 . . . 2 is derived as        follows, using lwipMpmCand[sizeId] as specified in Table 8-X2:        -   If candLwipModeA and candLwipModeB are both equal to −1, the            following applies:            candLwipModeList[0]=lwipMpmCand[sizeId][0]  (8-X1)            candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X2)            candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X3)        -   Otherwise, the following applies:            -   If candLwipModeA is equal to candLwipModeB or if either                candLwipModeA or candLwipModeB is equal to −1, the                following applies:                candLwipModeList[0]=(candLwipModeA!=−1)?candLwipModeA:candLwipModeB                  (8-X4)                -   If candLwipModeList[0] is equal to                    lwipMpmCand[sizeId][0], the following applies:                    candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X5)                    candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X6)                -   Otherwise, the following applies:                    candLwipModeList[1]=lwipMpmCand[sizeId][0]  (8-X7)                    candLwipModeList[2]=(candLwipModeList[0]!=lwipMpmCand[sizeId][1])?lwipMpmCand[sizeId][1]:lwipMpmCand[sizeId][2]  (8-X8)        -   Otherwise, the following applies:            candLwipModeList[0]=candLwipModeA  (8-X9)            candLwipModeList[1]=candLwipModeB  (8-X10)            -   If candLwipModeA and candLwipModeB are both not equal to                lwipMpmCand[sizeId][0], the following applies:                candLwipModeList[2]=lwipMpmCand[sizeId][0]  (8-X11)            -   Otherwise, the following applies:                -   If-candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][1], the following                    applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][1]  (8-X12)                -   Otherwise, the following applies:                    candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X13)    -   4. IntraPredModeY[xCb][yCb] is derived by applying the following        procedure:        -   If intra_lwip_mpm_flag[xCb][yCb] is equal to 1, the            IntraPredModeY[xCb][yCb] is set equal to            candLwipModeList[intra_lwip_mpm_idx[xCb][yCb]].        -   Otherwise, IntraPredModeY[xCb][yCb] is derived by applying            the following ordered steps:            -   1. When candLwipModeList[i] is greater than                candLwipModeList[j] for i=0 . . . 1 and for each i,                j=(i+1) . . . 2, both values are swapped as follows:                (candLwipModeList[i],candLwipModeList[j])=Swap(candLwipModeList[i],candLwipModeList[j])  (8-X14)            -   2. IntraPredModeY[xCb][yCb] is derived by the following                ordered steps:                -   i. IntraPredModeY[xCb][yCb] is set equal to                    intra_lwip_mpm_remainder[xCb][yCb].                -   ii. For i equal to 0 to 2, inclusive, when                    IntraPredModeY[xCb][yCb] is greater than or equal to                    candLwipModeList[i], the value of                    IntraPredModeY[xCb][yCb] is incremented by one.                    The variable IntraPredModeY[x][y] with x=xCb . . .                    xCbcbWidth−1 and y=yCb . . . yCb+cbHeight−1 is set                    to be equal to IntraPredModeY[xCb][yCb].                    8.4.X.1 Derivation process for prediction block size                    type                    Input to this process are:    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        Output of this process is a variable sizeId.        The variable sizeId is derived as follows:    -   If both cbWidth and cbHeight are equal to 4, sizeId is set equal        to 0.    -   Otherwise, if both cbWidth and cbHeight are less than or equal        to 8, sizeId is set equal to 1.    -   Otherwise, sizeId is set equal to 2.

TABLE 8-X1 Specification of mapping between intra prediction and affinelinear weighted intra prediction modes block size type sizeIdIntraPredModeY[xNbX][yNbX] 0 1 2 0  17 0 5 1  17 0 1 2, 3 17 10 3 4, 5 910 3 6, 7 9 10 3 8, 9 9 10 3 10, 11 9 10 0 12, 13 17 4 0 14, 15 17 6 016, 17 17 7 4 18, 19 17 7 4 20, 21 17 7 4 22, 23 17 5 5 24, 25 17 5 126, 27 5 0 1 28, 29 5 0 1 30, 31 5 3 1 32, 33 5 3 1 34, 35 34 12 6 36,37 22 12 6 38, 39 22 12 6 40, 41 22 12 6 42, 43 22 14 6 44, 45 34 14 1046, 47 34 14 10 48, 49 34 16 9 50, 51 34 16 9 52, 53 34 16 9 54, 55 3415 9 56, 57 34 13 9 58, 59 26 1 8 60, 61 26 1 8 62, 63 26 1 8 64, 65 261 8 66    26 1 8

TABLE 8-X2 Specification of affine linear weighted intra predictioncandidate modes candidate mode 0 1 2 lwipMpmCand[0] 17 34 5lwipMpmCand[1] 0 7 16 lwipMpmCand[2] 1 4 6<end>8.4.2. Derivation Process for Luma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

In this process, the luma intra prediction mode IntraPredModeY[xCb][yCb]is derived.

-   Table 8-1 specifies the value for the intra prediction mode    IntraPredModeY[xCb][yCb] and the associated names.

TABLE 8-1 Specification of intra prediction mode and associated namesIntra prediction mode Associated name 0   INTRA_PLANAR 1   INTRA_DC2..66 INTRA_ANGULAR2..INTRA_ANGULAR66 81..83 INTRA_LT_CCLM,INTRA_L_CCLM, INTRA_T_CCLM

-   -   NOTE—: The intra prediction modes INTRA_LT_CCLM, INTRA__L_CCLM        and INTRA__T_CCLM are only applicable to chroma components.

IntraPredModeY[xCb][yCb] is derived by the following ordered steps:

-   -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb+cbHeight−1) and (xCb+cbWidth−1, yCb−1),        respectively.    -   2. For X being replaced by either A or B, the variables        candIntraPredModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause <begin>6.4.X [Ed. (BB): Neighboring blocks            availability checking process tbd]<end> is invoked with the            location (xCurr, yCurr) set equal to (xCb, yCb) and the            neighboring location (xNbY, yNbY) set equal to (xNbX, yNbX)            as inputs, and the output is assigned to availableX.        -   The candidate intra prediction mode candIntraPredModeX is            derived as follows:            -   If one or more of the following conditions are true,                candIntraPredModeX is set equal to INTRA_PLANAR.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                    and ciip_flag[xNbX][yNbX] is not equal to 1.                -   pcm_flag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than ((yCb>>Ctb                    Log 2SizeY)<<Ctb Log 2SizeY).            -   Otherwise, candIntraPredModeX is derived as follows:                -   If intra_lwip_flag[xCb][yCb] is equal to 1,                    candIntraPredModeX is derived by the following                    ordered steps:                -    i. The size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the current coding block in luma samples                    cbWidth and the height of the current coding block                    in luma samples cbHeight as input, and the output is                    assigned to variable sizeId.                -    ii. candIntraPredModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X3.            -   Otherwise, candIntraPredModeX is set equal to                IntraPredModeY[xNbX][yNbX].    -   3. The variables ispDefaultMode1 and ispDefaultMode2 are defined        as follows:        -   If IntraSubPartitionsSplitType is equal to ISP_HOR_SPLIT,            ispDefaultMode1 is set equal to INTRA_ANGULAR18 and            ispDefaultMode2 is set equal to INTRA_ANGULAR5.        -   Otherwise, ispDefaultMode1 is set equal to INTRA_ANGULAR50            and ispDefaultMode2 is set equal to INTRA_ANGULAR63.

TABLE 8-X3 Specification of mapping between affine linear weighted intraprediction and intra prediction modes block size type sizeIdIntraPredModeY[xNbX][yNbX] 0 1 2 0 0 0 1 1 18 1 1 2 18 0 1 3 0 1 1 4 180 18 5 0 22 0 6 12 18 1 7 0 18 0 8 18 1 1 9 2 0 50 10 18 1 0 11 12 0 1218 1 13 18 0 14 1 44 15 18 0 16 18 50 17 0 1 18 0 0 19 50 20 0 21 50 220 23 56 24 0 25 50 26 66 27 50 28 56 29 50 30 50 31 1 32 50 33 50 34 508.4.3 Derivation Process for Chroma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current chroma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

In this process, the chroma intra prediction modeIntraPredModeC[xCb][yCb] is derived.

The corresponding luma intra prediction mode lumaIntraPredMode isderived as follows:

-   -   If intra_lwip_flag[xCb][yCb] is equal to 1, lumaIntraPredMode is        derived by the following ordered steps:        -   i. The size type derivation process for a block as specified            in clause 8.4.X.1 is invoked with the width of the current            coding block in luma samples cbWidth and the height of the            current coding block in luma samples cbHeight as input, and            the output is assigned to variable sizeId.        -   ii. The luma intra prediction mode is derived using            IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] and sizeId as            specified in Table 8-X3 and assigning the value of            candIntraPredModeX to lumaIntraPredMode.    -   Otherwise, lumaIntraPredMode is set equal to        IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

The chroma intra prediction mode IntraPredModeC[xCb][yCb] is derivedusing intra_chroma_pred_mode[xCb][yCb] and lumaIntraPredMode asspecified in Table 8-2 and Table 8-3.

. . .

xxx. Intra Sample Prediction

<begin>

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable nCbW specifying the coding block width,    -   a variable nCbH specifying the coding block height,    -   a variable cldx specifying the colour component of the current        block.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The predicted samples predSamples[x][y] are derived as follows:

-   -   If intra_lwip_flag[xTbCmp][yTbCmp] is equal to 1 and cldx is        equal to 0, the affine linear weighted intra sample prediction        process as specified in clause 8.4.4.2.X1 is invoked with the        location (xTbCmp, yTbCmp), the intra prediction mode        predModeIntra, the transform block width nTbW and height nTbH as        inputs, and the output is predSamples.    -   Otherwise, the general intra sample prediction process as        specified in clause 8.4.4.2.X1. is invoked with the location        (xTbCmp, yTbCmp), the intra prediction mode predModeIntra, the        transform block width nTbW and height nTbH, the coding block        width nCbW and height nCbH, and the variable cldx as inputs, and        the output is predSamples.        8.4.4.2.X1Affine Linear Weighted Intra Sample Prediction

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The size type derivation process for a block as specified in clause8.4.X.1 is invoked with the transform block width nTbW and the transformblock height nTbH as input, and the output is assigned to variablesizeId.

Variables numModes, boundarySize, predW, predH and predC are derivedusing sizeId as specified in Table 8-X4.

TABLE 8-X4 Specification of number of modes, boundary sample size andprediction sizes depending on sizeId sizeId numModes boundarySize predWpredH predC 0 35 2 4 4 4 1 19 4 4 4 4 2 11 4 Min(nTbW, 8) Min(nTbH, 8) 8

The flag isTransposed is derived as follows:isTransposed=(predModeIntra>(numModes/2))?1:0  (8-X15)

The flags needUpsBdryHor and needUpsBdryVer are derived as follows:needUpsBdryHor=(nTbW>predW)?TRUE:FALSE  (8-X16)needUpsBdryVer=(nTbH>predH)?TRUE:FALSE  (8-X17)

The variables upsBdryW and upsBdryH are derived as follows:upsBdryW=(nTbH>nTbW)?nTbW:predW  (8-X18)upsBdryH=(nTbH>nTbW)?predH:nTbH  (8-X19)

The variables lwipW and lwipH are derived as follows:lwipW=(isTransposed==1)?predH:predW  (8-X20)lwipH=(isTransposed==1)?predW:predH  (8-X21)

For the generation of the reference samples refT[x] with x=0 . . .nTbW−1 and refL[y] with y=0 . . . nTbH−1, the reference samplederivation process as specified in clause 8.4.4.2.X2 is invoked with thesample location (xTbCmp, yTbCmp), the transform block width nTbW, thetransform block height nTbH as inputs, and top and left referencesamples refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1,respectively, as outputs.

For the generation of the boundary samples p[x] with x=0 . . .2*boundarySize−1, the following applies:

-   -   The boundary reduction process as specified in clause 8.4.4.2.X3        is invoked for the top reference samples with the block size        nTbW, the reference samples refT, the boundary size        boundarySize, the upsampling boundary flag needUpsBdryVer, and        the upsampling boundary size upsBdryW as inputs, and reduced        boundary samples redT[x] with x=0 . . . boundarySize−1 and        upsampling boundary samples upsBdryT[x] with x=0 . . .        upsBdryW−1 as outputs.    -   The boundary reduction process as specified in clause 8.4.4.2.X3        is invoked for the left reference samples with the block size        nTbH, the reference samples refL, the boundary size        boundarySize, the upsampling boundary flag needUpsBdryHor, and        the upsampling boundary size upsBdryH as inputs, and reduced        boundary samples redL[x] with x=0 . . . boundarySize−1 and        upsampling boundary samples upsBdryL[x] with x=0 . . .        upsBdryH−1 as outputs.    -   The reduced top and left boundary samples redT and redL are        assigned to the boundary sample array p as follows:        -   If isTransposed is equal to 1, p[x] is set equal to redL[x]            with x=0 . . . boundarySize−1 and p[x+boundarySize] is set            equal to redT[x] with x=0 . . . boundarySize−1.        -   Otherwise, p[x] is set equal to redT[x] with x=0 . . .            boundarySize−1 and p[x+boundarySize] is set equal to redL[x]            with x=0 . . . boundarySize−1.

For the intra sample prediction process according to predModeIntra, thefollowing ordered steps apply:

-   -   1. The affine linear weighted samples predLwip[x][y], with x=0 .        . . lwipW−1, y=0 . . . lwipH−1 are derived as follows:        -   The variable modeId is derived as follows:            modeId=predModeIntra−(isTransposed==1)?(numModes/2):0  (8-X22)        -   The weight matrix mWeight[x][y] with x=0 . . .            2*boundarySize−1, y=0 . . . predC*predC−1 is derived using            sizeId and modeId as specified in Table 8-XX [TBD: add            weight matrices].        -   The bias vector vBias[y] with y=0 . . . predC*predC−1 is            derived using sizeId and modeId as specified in Table 8-XX            [TBD: add bias vectors].        -   The variable sW is derived using sizeId and modeId as            specified in Table 8-X5.        -   The affine linear weighted samples predLwip[x][y], with x=0            . . . lwipW−1, y=0 . . . lwipH−1 are derived as follows:

$\begin{matrix}{\mspace{79mu}{{oW} = {1\text{<<}\left( {{sW} - 1} \right)}}} & \left( {8\text{-}{X23}} \right) \\{\mspace{79mu}{{sB} = {{BitDepth}_{Y} - 1}}} & \left( {8\text{-}{X24}} \right) \\{\mspace{79mu}{{i{ncW}} = {{\left( {{predC} > {lwipW}} \right)?2}\text{:}1}}} & \left( {8\text{-}{X25}} \right) \\{\mspace{79mu}{{{i{nc}}\; H} = {{\left( {{predC} > {lwipH}} \right)?2}\text{:}1}}} & \left( {8\text{-}{X26}} \right) \\{{{{predLwip}\lbrack x\rbrack}\lbrack y\rbrack} = {\left( {\left( {\sum\limits_{i = 0}^{{2*{boundarySize}} - 1}\;{{{{mWeight}\lbrack i\rbrack}\left\lbrack {{y*{incH}*{predC}} + {x*{incW}}} \right\rbrack}*{p\lbrack i\rbrack}}} \right) + \left( {{{vBias}\left\lbrack {{y*{incH}*{predC}} + {x*{incW}}} \right\rbrack}{\operatorname{<<}{sB}}} \right) + {oW}} \right)\text{>>}{sW}}} & \left( {8\text{-}{X27}} \right)\end{matrix}$

-   -   2. The predicted samples predSamples[x][y], with x=0 . . .        nTbW−1, y=0 . . . nTbH−1 are derived as follows:        -   When isTransposed is equal to 1, predLwip[x][y], with x=0 .            . . predW−1, y=0 . . . predH−1 is set equal to            predLwip[y][x].        -   If needUpsBdryVer is equal to TRUE or needUpsBdryHor is            equal to TRUE, the prediction upsampling process as            specified in clause 8.4.4.2.X4 is invoked with the input            block width predW, the input block height predH, affine            linear weighted samples predLwip, the transform block width            nTbW, the transform block height nTbH, the upsampling            boundary width upsBdryW, the upsampling boundary height            upsBdryH, the top upsampling boundary samples upsBdryT, and            the left upsampling boundary samples upsBdryL as inputs, and            the output is the predicted sample array predSamples.        -   Otherwise, predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .            . nTbH−1 is set equal to predLwip[x][y].

TABLE 8-X5 Specification of weight shifts sW depending on sizeId andmodeId modeId sizeId 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 0 8 8 88 8 8 8 8 8 8 8 8 8 8 8 8 8 8 1 8 8 8 9 8 8 8 8 9 8 2 8 8 8 8 8 88.4.4.2.X2Reference Sample Derivation Process

Inputs to this process are:

-   -   a sample location (xTbY, yTbY) specifying the top-left luma        sample of the current transform block relative to the top-left        luma sample of the current picture,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height.

Outputs of this process are the top and left reference samples refT[x]with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1, respectively.

The neighboring samples refT[x] with x=0 . . . nTbW−1 and refL[y] withy=0 . . . nTbH−1 are constructed samples prior to the in-loop filterprocess and derived as follows:

-   -   The top and left neighboring luma locations (xNbT, yNbT) and        (xNbL, yNbL) are specified by:        (xNbT,yNbT)=(xTbY+x,yTbY−1)  (8-X28)        (xNbL,yNbL)=(xTbY−1,yTbY+y)  (8-X29)    -   The availability derivation process for a block as specified in        clause 6.4.X [Ed. (BB): Neighboring blocks availability checking        process tbd] is invoked with the current luma location (xCurr,        yCurr) set equal to (xTbY, yTbY) and the top neighboring luma        location (xNbT, yNbT) as inputs, and the output is assigned to        availTop[x] with x=0 . . . nTbW−1.    -   The availability derivation process for a block as specified in        clause 6.4.X [Ed. (BB): Neighboring blocks availability checking        process tbd] is invoked with the current luma location (xCurr,        yCurr) set equal to (xTbY, yTbY) and the left neighboring luma        location (xNbL, yNbL) as inputs, and the output is assigned to        availLeft[y] with y=0 . . . nTbH−1.    -   The top reference samples refT[x] with x=0 . . . nTbW−1 are        derived as follows:        -   If all availTop[x] with x=0 . . . nTbW−1 are equal to TRUE,            the sample at the location (xNbT, yNbT) is assigned to            refT[x] with x=0 . . . nTbW−1.        -   Otherwise, if availTop[0] is equal to FALSE, all refT[x]            with x=0 . . . nTbW−1 are set equal to I<<(BitDepthγ−1).        -   Otherwise, reference samples refT[x] with x=0 . . . nTbW−1            are derived by the following ordered steps:            -   1. The variable lastT is set equal to the position x of                the first element in the sequence availTop[x] with x=1 .                . . nTbW−1 that is equal to FALSE.            -   2. For every x=0 . . . lastT−1, the sample at the                location (xNbT, yNbT) is assigned to refT[x].            -   3. For every x=lastT . . . nTbW−1, refT[x] is set equal                to refT[lastT−1].    -   The left reference samples refL[y] with x=0 . . . nTbH−1 are        derived as follows:        -   If all availLeft[y] with yz=0 . . . nTbH−1 are equal to            TRUE, the sample at the location (xNbL, yNbL) is assigned to            refL[y] with y=0 . . . nTbH−1.        -   Otherwise, if availLeft[0] is equal to FALSE, all refL[y]            with y=0 . . . nTbH−1 are set equal to 1<<(BitDepth_(Y)−1).        -   Otherwise, reference samples refL[y] with y=0 . . . nTbH−1            are derived by the following ordered steps:            -   1. The variable lastL is set equal to the position y of                the first element in the sequence availLeft[y] with y=1                . . . nTbH−1 that is equal to FALSE.            -   2. For every y=0 . . . lastL−1, the sample at the                location (xNbL, yNbL) is assigned to refL[y].            -   3. For every y=lastL . . . nTbH−1, refL[y] is set equal                to refL[lastL−1].                Specification of the boundary reduction process

Inputs to this process are:

-   -   a variable nTbX specifying the transform block size,    -   reference samples refX[x] with x=0 . . . nTbX−1,    -   a variable boundarySize specifying the downsampled boundary        size,    -   a flag needUpsBdryX specifying whether intermediate boundary        samples are required for upsampling,    -   a variable upsBdrySize specifying the boundary size for        upsampling.

Outputs of this process are the reduced boundary samples redX[x] withx=0 . . . boundarySize−1 and upsampling boundary samples upsBdryX[x]with x=0 . . . upsBdrySize−1.

The upsampling boundary samples upsBdryX[x] with x=0 . . . upsBdrySize−1are derived as follows:

-   -   If needUpsBdryX is equal to TRUE and upsBdrySize is less than        nTbX, the following applies:        uDwn=nTbX/upsBdrySize  (8-X30)        upsBdryX[x]=(Σ_(i=0) ^(uDwn-1)refX[x*uDwn+i]+(1<<(Log        2(uDwn)−1)))>>Log 2(uDwn)   (8-X31)    -   Otherwise (upsBdrySize is equal to nTbX), upsBdryX[x] is set        equal to refX[x].

The reduced boundary samples redX[x] with x=0 . . . boundarySize−1 arederived as follows:

-   -   If boundarySize is less than upsBdrySize, the following applies:        bDwn=upsBdrySize/boundarySize  (8-X32)        redX[x]=(Σ_(i=0) ^(bDwn-1)upsBdryX[x*bDwn+i]+(1<<(Log        2(bDwn)−1)))>>Log 2(bDwn)   (8-X33)    -   Otherwise (boundarySize is equal to upsBdrySize), redX[x] is set        equal to upsBdryX[x].        8.4.4.2.X4Specification of the Prediction Upsampling Process        Inputs to this process are:    -   a variable predW specifying the input block width,    -   a variable predH specifying the input block height,    -   affine linear weighted samples predLwip[x][y], with x=0 . . .        predW−1, y=0 . . . predH−1,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable upsBdryW specifying the upsampling boundary width,    -   a variable upsBdryH specifying the upsampling boundary height,    -   top upsampling boundary samples upsBdryT[x] with x=0 . . .        upsBdryW−1,    -   left upsampling boundary samples upsBdryL[x] with x=0 . . .        upsBdryH−1.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The sparse predicted samples predSamples[m][n] are derived frompredLwip[x][y], with x=0 . . . predW−1, y=0 . . . predH−1 as follows:upHor=nTbW/predW  (8-X34)upVer=nTbH/predH  (8-X35)predSamples[(x+1)*upHor−1][(y+1)*upVer−1]=predLwip[x][y]  (8-X36)

The top boundary samples upsBdryT[x] with x=0 . . . upsBdryW−1 areassigned to predSamples[m][−1] as follows:predSamples[(x−1)*(nTbW/upsBdryW)−1][−1]=upsBdryL[y]  (8-X37)

The left boundary samples upsBdryL[y] with y=0 . . . upsBdryH−1 areassigned to predSamples[−1][n] as follows:predSamples[−1][(y+1)*(nTbH/upsBdryH)−1]=upsBdryL[y]  (8-X38)

The predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .. nTbH−1 are derived as follows:

-   -   If nTbH is greater than nTbW, the following ordered steps apply:    -   1. When upHor is greater than 1, horizontal upsampling for all        sparse positions (xHor, yHor)=(m*upHor−1, n*upVer−1) with m=0 .        . . predW−1, n=1 . . . predH is applied with dX=1 . . . upHor−1        as follows:        predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor])/upHor  (8-X39)    -   2. Vertical upsampling for all sparse positions (xVer, yVer)=(m,        n*upVer−1) with m=0 . . . nTbW−1, n=0 . . . predH−1 is applied        with dY=1 . . . upVer−1 as follows:        predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer])/upVer  (8-X40)    -   Otherwise, the following ordered steps apply:    -   1. When upVer is greater than 1, vertical upsampling for all        sparse positions (xVer, yVer)=(m*upHor−1, n*upVer−1) with m=1 .        . . predW, n=0 . . . predH−1 is applied with dY=1 . . . upVer−1        as specified in (8-X40).    -   2. Horizontal upsampling for all sparse positions (xHor,        yHor)=(m*upHor−1, n) with m=0 . . . predW−1, n=0 . . . nTbH−1 is        applied with dX=1 . . . upHor−1 as specified in (8-X39).        <end>

TABLE 9-9 Syntax elements and associated binarizations BinarizationSyntax structure Syntax element Process Input parameters coding_unit( )cu_skip_flag[ ][ ] FL cMax = 1 pred_mode_ibc_flag FL cMax = 1pred_mode_flag FL cMax = 1 <begin>intra_lwip_flag[ ][ ] FL cMax = 1intra_lwip_mpm_flag[ ][ ] FL cMax = 1 intra_lwip_mpm_idx[ ][ ] TR cMax =2, cRiceParam = 0 intra_lwip_mpm_remainder[ ][ ] FL cMax = (cbWidth = =4 && cbHeight = = 4) ? 31 : ( (cbWidth <= 8 && cbHeight <= 8) ? 15 : 7)...

TABLE 9-15 Assignment of ctxInc to syntax elements with context codedbins binldx Syntax element 0 1 2 3 4 >= 5 ... terminate na na na na naintra_lwip_flag[ ][ ] (Abs ( Log2 (cbWidth) - na na na na na Log2(cbHeight) ) > 1) ? 3 : ( 0, 1, 2 (clause 9.5.4.2.2) )intra_lwip_mpm_flag[ ][ ] 0 na na na na na intra_lwip_mpm_idx[ ][ ]bypass bypass na na na na intra_lwip_mpm_remainder[ ][ ] bypass bypassbypass bypass bypass na

TABLE 9-16 Specification of ctxInc using left and above syntax elementsSyntax element condL condA ctxSetIdx ... intra_lwip_flag[x0][y0]intra_lwip_flag[xNbL][yNbL] intra_lwip_flag[xNbA][yNbA] 0 ...<end>Summary of ALWIP

For predicting the samples of a rectangular block of width W and heightH, affine linear weighted intra prediction (ALWIP) takes one line of Hreconstructed neighboring boundary samples left of the block and oneline of W reconstructed neighboring boundary samples above the block asinput. If the reconstructed samples are unavailable, they are generatedas it is done in the conventional intra prediction. ALWIP is onlyapplied to luma intra block. For chroma intra block, the conventionalintra coding modes are applied.

The generation of the prediction signal is based on the following threesteps:

-   -   1. Out of the boundary samples, four samples in the case of        W=H=4 and eight samples in all other cases are extracted by        averaging.    -   2. A matrix vector multiplication, followed by addition of an        offset, is carried out with the averaged samples as an input.        The result is a reduced prediction signal on a subsampled set of        samples in the original block.    -   3. The prediction signal at the remaining positions is generated        from the prediction signal on the subsampled set by linear        interpolation which is a single step linear interpolation in        each direction.

If an ALWIP mode is to be applied, the index predmode of the ALWIP modeis signaled using a MPM-list with 3 MPMS. Here, the derivation of theMPMs is performed using the intra-modes of the above and the left PU asfollows. There are three fixed tables map_angular_to_alwip_(idx), idx ∈{0, 1, 2} that assign to each conventional intra prediction modepredmode_(Angular) an ALWIP modepredmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an indexidx(PU)=idx(W,H)∈{0,1,2}

that indicates from which of the three sets the ALWIP-parameters are tobe taken.

If the above Prediction Unit PU_(above) is available, belongs to thesame CTU as the current PU and is in intra mode, if idx(PU)=idx(PUabove) above) and if ALWIP is applied on PU_(above) with ALWIP-modepredmode_(ALWIP) ^(above), one puts

mode_(ALWIP)^(above) = predmode_(ALWIP)^(above).

If the above PU is available, belongs to the same CTU as the current PUand is in intra mode and if a conventional intra prediction modepredmode_(Angular) ^(above) is applied on the above PU, one putsmode_(ALWIP) ^(above)=map_angular_to_alwip_(idx(PU) _(above))[predmode_(Angular) ^(above)].In all other cases, one putsmode_(ALWIP) ^(above)=−1

which means that this mode is unavailable. In the same way but withoutthe restriction that the left PU needs to belong to the same CTU as thecurrent PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx ∈{0, 1, 2} areprovided, each of which contains three distinct ALWIP modes. Out of thedefault list list_(idx(PU)) and the modes mode_(ALWIP) ^(above) andmode_(ALWIP) ^(left), one constructs three distinct MPMs by substituting−1 by default values as well as eliminating repetitions.

For the luma MPM-list derivation, whenever a neighboring luma block isencountered which uses an ALWIP-mode predmode_(ALWIP), this block istreated as if it was using the conventional intra-prediction modepredmode_(Angular).predmode_(Angular)=map_alwip_to_angular_(idx(PU))[predmode_(ALWIP)]3 Transform in VVC3.1 Multiple Transform Selection (MTS)

In addition to DCT-II which has been employed in HEVC, a MultipleTransform Selection (MTS) scheme is used for residual coding both interand intra coded blocks. It uses multiple selected transforms from theDCT8/DST7. The newly introduced transform matrices are DST-VII andDCT-VIII.

3.2 Reduced Secondary Transform (RST) Proposed in JVET-N0193

Reduced secondary transform (RST) applies 16×16 and 16×64 non-separabletransform for 4×4 and 8×8 blocks, respectively. Primary forward andinverse transforms are still performed the same way as two 1-Dhorizontal/vertical transform passes. Secondary forward and inversetransforms are a separate process step from that of primary transforms.For encoder, primary forward transform is performed first, then followedby secondary forward transform and quantization, and CABAC bit encoding.For decoder, CABAC bit decoding and inverse quantization, then Secondaryinverse transform is performed first, then followed by primary inversetransform. RST applies only to intra coded TUs in both intra slice andinter slices.

3.3 A Unified MPM List for Intra Mode Coding in JVET-N0185

A unified 6-MPM list is proposed for intra blocks irrespective ofwhether Multiple Reference Line (MRL) and Intra sub-partition (ISP)coding tools are applied or not. The MPM list is constructed based onintra modes of the left and above neighboring block as in VTM4.0.Suppose the mode of the left is denoted as Left and the mode of theabove block is denoted as Above, the unified MPM list is constructed asfollows:

-   -   When a neighboring block is not available, its intra mode is set        to Planar by default.    -   If both modes Left and Above are non-angular modes:    -   a. MPM list→{Planar, DC, V, H, V−4, V+4}    -   If one of modes Left and Above is angular mode, and the other is        non-angular:    -   a. Set a mode Max as the larger mode in Left and Above    -   b. MPM list→{Planar, Max, DC, Max−1, Max+1, Max−2}    -   If Left and Above are both angular and they are different:    -   a. Set a mode Max as the larger mode in Left and Above    -   b. if the difference of mode Left and Above is in the range of 2        to 62, inclusive        -   i. MPM list→{Planar, Left, Above, DC, Max−1, Max+1}    -   c. Otherwise        -   i. MPM list→{Planar, Left, Above, DC, Max−2, Max+2}    -   If Left and Above are both angular and they are the same:    -   a. MPM list→{Planar, Left, Left−1, Left+1, DC, Left−2}

Besides, the first bin of the MPM index codeword is CABAC context coded.In total three contexts are used, corresponding to whether the currentintra block is MRL enabled, ISP enabled, or a normal intra block.

The left neighboring block and above neighboring block used in theunified MPM list construction is A2 and B2 as shown in FIG. 10.

One MPM flag is firstly coded. If the block is coded with one of mode inthe MPM list, an MPM index is further coded. Otherwise, an index to theremaining modes (excluding MPMs) is coded.

4 Examples of Drawbacks in Existing Implementations

The design of ALWIP in JVET-N0217 has the following problems:

-   -   1) At the March 2019 JVET meeting, a unified 6-MPM list        generation was adopted for MRL mode, ISP mode, and normal intra        mode. But the affine linear weighted prediction mode uses a        different 3-MPM list construction which makes the MPM list        construction complicated. A complex MPM list construction might        compromise the throughput of the decoder, in particular for        small blocks such as 4×4 samples.    -   2) ALWIP is only applied to luma component of the block. For the        chroma component of an ALWP coded block, a chroma mode index is        coded and sent to decoder, which could result in unnecessary        signaling.    -   3) The interactions of ALWIP with other coding tools should be        considered.    -   4) When calculating upsBdryX in upsBdryX[x]=(Σ_(i=0) ^(uDwn-1)        RefX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log 2(uDwn) (8-X31), it is        possible that Log 2(uDwn)−1 is equal to −1, while left shifted        with −1 is undefined.    -   5) When upsampling the prediction samples, no rounding is        applied.    -   6) In the deblocking process, ALWIP coded blocks are treated as        normal intra-blocks.        5) Exemplary Methods for Matrix-Based Intra Coding

Embodiments of the presently disclosed technology overcome drawbacks ofexisting implementations, thereby providing video coding with highercoding efficiencies but lower computational complexity. Matrix-basedintra prediction methods for video coding, and as described in thepresent document, may enhance both existing and future video codingstandards, is elucidated in the following examples described for variousimplementations. The examples of the disclosed technology provided belowexplain general concepts and are not meant to be interpreted aslimiting. In an example, unless explicitly indicated to the contrary,the various features described in these examples may be combined.

In the following discussion, an intra-prediction mode refers to anangular intra prediction mode (including DC, planar, CCLM and otherpossible intra prediction modes); while an intra mode refers to normalintra mode, or MRL, or ISP or ALWIP.

In the following discussion, “Other intra modes” may refer to one ormultiple intra modes except ALWIP, such as normal intra mode, or MRL, orISP.

In the following discussion, SatShift(x, n) is defined as

${{SatShift}\left( {x,n} \right)} = \left\{ \begin{matrix}{{\left( {x + {{offsset}\; 0}} \right)\operatorname{>>}n}\mspace{14mu}} & {{{if}\mspace{14mu} x} \geq 0} \\{{- \left( {\left( {{- x} + {{offset}\; 1}} \right)\operatorname{>>}n} \right)}\mspace{14mu}} & {{{if}\mspace{14mu} x} < 0}\end{matrix} \right.$

Shift(x, n) is defined as Shift(x, n)=(x+offset0)>>n.

In one example, offset0 and/or offset1 are set to (1<<n)>>1 or(1<<(n−1)). In another example, offset0 and/or offset1 are set to 0.

In another example, offset0=offset1=((1<<n)>>1)−1 or ((1<<(n−1)))−1.

Clip3(min, max, x) is defined as

${{Clip}\; 3\left( {{Min},{Max},x} \right)} = \left\{ \begin{matrix}{{Min}\mspace{20mu}} & {{{if}\ x} < {Min}} \\{{Max}\mspace{20mu}} & {{{if}\ x} > {Max}} \\{x\ } & {Otherwise}\end{matrix} \right.$MPM List Construction for ALWIP

-   -   1. It is proposed that the whole or partial of the MPM list for        ALWIP may be constructed according to the whole or partial        procedure to construct the MPM list for non-ALWIP intra mode        (such as normal intra mode, MRL, or ISP).        -   a. In one example, the size of the MPM list for ALWIP may be            the same as that of the MPM list for non-ALWIP intra mode.            -   i. For example, the size of MPM list is 6 for both ALWIP                and non-ALWIP intra modes.        -   b. In one example, the MPM list for ALWIP may be derived            from the MPM list for non-ALWIP intra mode.            -   i. In one example, the MPM list for non-ALWIP intra mode                may be firstly constructed. Afterwards, partial or all                of them may be converted to the MPMs which may be                further added to the MPM list for ALWIP coded blocks.                -   1) Alternatively, furthermore, when adding a                    converted MPM to the MPM list for ALWIP coded                    blocks, pruning may be applied.                -   2) Default modes may be added to the MPM list for                    ALWIP coded blocks.                -    a. In one example, default modes may be added                    before those converted from the MPM list of                    non-ALWIP intra mode.                -    b. Alternatively, default modes may be added after                    those converted from the MPM list of non-ALWIP intra                    mode.                -    c. Alternatively, default modes may be added in an                    interleaved way with those converted from the MPM                    list of non-ALWIP intra mode.                -    d. In one example, the default modes may be fixed                    to be the same for all kinds of blocks.                -    e. Alternatively, the default modes may be                    determined according to coded information, such as                    availability of neighboring blocks, mode information                    of neighboring blocks, block dimension.            -   ii. In one example, one intra-prediction mode in the MPM                list for non-ALWIP intra mode may be converted to its                corresponding ALWIP intra-prediction mode, when it is                put into the MPM list for ALWIP.                -   1) Alternatively, all the intra-prediction modes in                    the MPM list for non-ALWIP intra modes may be                    converted to corresponding ALWIP intra-prediction                    modes before being used to construct the MPM list                    for ALWIP.                -   2) Alternatively, all the candidate intra-prediction                    modes (may include the intra-prediction modes from                    neighboring blocks and default intra-prediction                    modes such as Planar and DC) may be converted to                    corresponding ALWIP intra-prediction modes before                    being used to construct the MPM list for non-ALWIP                    intra modes, if the MPM list for non-ALWIP intra                    modes may be further used to derive the MPM list for                    ALWIP.                -   3) In one example, two converted ALWIP                    intra-prediction modes may be compared.                -    a. In one example, if they are the same, only one                    of them may be put into the MPM list for ALWIP.                -    b. In one example, if they are the same, only one                    of them may be put into the MPM list for non-ALWIP                    intra modes.            -   iii. In one example, K out of S intra-prediction modes                in the MPM list for non-ALWIP intra modes may be picked                as the MPM list for ALWIP mode. E.g., K is equal to 3                and S is equal to 6.                -   1) In one example, the first K intra-prediction                    modes in the MPM list for non-ALWIP intra modes may                    be picked as the MPM list for ALWIP mode.    -   2. It is proposed that the one or multiple neighboring blocks        used to derive the MPM list for ALWIP may also be used to used        derive the MPM list for non-ALWIP intra modes (such as normal        intra mode, MRL, or ISP).        -   a. In one example, the neighboring block left to the current            block used to derive the MPM list for ALWIP should be the            same as that used to derive the MPM list for non-ALWIP intra            modes.            -   i. Suppose the top-left corner of the current block is                (xCb, yCb), the width and height of the current block                are W and H, then in one example, the left neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb−1,                yCb). In an alternative example, the left neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb−1,                yCb+H−1).            -   ii. For example, the left neighboring block and above                neighboring block used in the unified MPM list                construction is A2 and B2 as shown in FIG. 10.        -   b. In one example, the neighboring block above to the            current block used to derive the MPM list for ALWIP should            be the same as that used to derive the MPM list for            non-ALWIP intra modes.            -   i. Suppose the top-left corner of the current block is                (xCb, yCb), the width and height of the current block                are W and H, then in one example, the above neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb,                yCb−1). In an alternative example, the above neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb+W−1,                yCb−1).            -   ii. For example, the left neighboring block and above                neighboring block used in the unified MPM list                construction is A1 and B1 as shown in FIG. 10.    -   3. It is proposed that the MPM list for ALWIP may be constructed        in different ways according to the width and/or height of the        current block.        -   a. In one example, different neighboring blocks may be            accessed for different block dimensions.    -   4. It is proposed that the MPM list for ALWIP and the MPM list        for non-ALWIP intra modes may be constructed with the same        procedure but with different parameters.        -   a. In one example, K out of S intra-prediction modes in the            MPM list construction procedure of non-ALWIP intra modes may            be derived for the MPM list used in ALWIP mode. E.g., K is            equal to 3 and S is equal to 6.            -   i. In one example, the first K intra-prediction modes in                the MPM list construction procedure may be derived for                the MPM list used in ALWIP mode.        -   b. In one example, the first mode in the MPM list may be            different.            -   i. For example, the first mode in the MPM list for                non-ALWIP intra modes may be Planar, but it may be a                Mode X0 in the MPM list for ALWIP.                -   1) In one example, X0 may be the ALWIP                    intra-prediction mode converted from Planar.        -   c. In one example, stuffing modes in the MPM list may be            different.            -   i. For example, the first three stuffing modes in the                MPM list for non-ALWIP intra modes may be DC, Vertical                and Horizontal, but they may be Mode X1, X2, X3 in the                MPM list for ALWIP.                -   1) In one example, X1, X2, X3 may be different for                    different sizeId.            -   ii. In one example, the number of stuffing mode may be                different.        -   d. In one example, neighboring modes in the MPM list may be            different.            -   i. For example, the normal intra-prediction modes of                neighboring blocks are used to construct the MPM list                for non-ALWIP intra modes. And they are converted to                ALWIP intra-prediction modes to construct the MPM list                for ALWIP mode.        -   e. In one example, the shifted modes in the MPM list may be            different.            -   i. For example, X+K0 where X is a normal                intra-prediction mode and K0 is an integer may be put                into the MPM list for non-ALWIP intra modes. And Y+K1                where Y is an ALWIP intra-prediction mode and K1 is an                integer may be put into the MPM list for ALWIP, where K0                may be different from K1.                -   1) In one example, K1 may depend on the width and                    height.    -   5. It is proposed that a neighboring block is treated as        unavailable if it is coded with ALWIP when constructing the MPM        list for the current block with non-ALWIP intra modes.        -   a. Alternatively, a neighboring block is treated as being            coded with a predefined intra-prediction mode (such as            Planar) if it is coded with ALWIP when constructing the MPM            list for the current block with non-ALWIP intra modes.    -   6. It is proposed that a neighboring block is treated as        unavailable if it is coded with non-ALWIP intra modes when        constructing the MPM list for the current block with ALWIP mode.        -   a. Alternatively, a neighboring block is treated as being            coded with a predefined ALWIP intra-prediction mode X if it            is coded with non-ALWIP intra modes when constructing the            MPM list for the current block with ALWIP mode.            -   i. In one example, X may depend on the block dimensions,                such as width and/or height.    -   7. It is proposed to remove the storage of ALWIP flag from line        buffer.        -   a. In one example, when the 2^(nd) block to be accessed is            located in a different LCU/CTU row/region compared to the            current block, the conditional check of whether the 2^(nd)            block is coded with ALWIP is skipped.        -   b. In one example, when the 2^(nd) block to be accessed is            located in a different LCU/CTU row/region compared to the            current block, the 2^(nd) block is treated in the same way            as non-ALWIP mode, such as treated as normal intra coded            block.    -   8. When encoding the ALWIP flag, no more than K (K>=0) contexts        may be used.        -   a. In one example, K=1.    -   9. It is proposed to store the converted intra prediction mode        of ALWIP coded blocks instead of directly storing the mode index        associated with the ALWIP mode.        -   a. In one example, the decoded mode index associated with            one ALWIP coded block is mapped to the normal intra mode,            such as according to map_alwip_to_angular as described in            Section 2.5.7.        -   b. Alternatively, furthermore, the storage of ALWIP flag is            totally removed.        -   c. Alternatively, furthermore, the storage of ALWIP mode is            totally removed.        -   d. Alternatively, furthermore, condition check of whether            one neighboring/current block is coded with ALWIP flag may            be skipped.        -   e. Alternatively, furthermore, the conversion of modes            assigned for ALWIP coded blocks and normal intra predictions            associated with one accessed block may be skipped.            ALWIP on Different Color Components    -   10. It is proposed that an inferred chroma intra mode (e.g., DM        mode) might be always applied if the corresponding luma block is        coded with ALWIP mode.        -   a. In one example, chroma intra mode is inferred to be DM            mode without signaling if the corresponding luma block is            coded with ALWIP mode.        -   b. In one example, the corresponding luma block may be the            one covering the corresponding sample of a chroma sample            located at a given position (e.g., top-left of current            chroma block, center of current chroma block).        -   c. In one example, the DM mode may be derived according to            the intra prediction mode of the corresponding luma block,            such as via mapping the (ALWIP) mode to one of the normal            intra mode.    -   11. When the corresponding luma block of the chroma blocks is        coded with ALWIP mode, several DM modes may be derived.    -   12. It is proposed that a special mode is assigned to the chroma        blocks if one corresponding luma block is coded with ALWIP mode.        -   a. In one example, the special mode is defined to be a given            normal intra prediction mode regardless the intra prediction            mode associated with the ALWIP coded blocks.        -   b. In one example, different ways of intra prediction may be            assigned to this special mode.    -   13. It is proposed that ALWIP may also be applied to chroma        components.        -   a. In one example, the matrix and/or bias vector may be            different for different color components.        -   b. In one example, the matrix and/or bias vector may be            predefined jointly for Cb and Cr.            -   i. In one example, Cb and Cr component may be                concatenated.            -   ii. In one example, Cb and Cr component may be                interleaved.        -   c. In one example, the chroma component may share the same            ALWIP intra-prediction mode as the corresponding luma block.            -   i. In one example, the same ALWIP intra-prediction mode                is applied on the chroma component if the corresponding                luma block applies the ALWIP mode and the chroma block                is coded with DM mode.            -   ii. In one example, the same ALWIP intra-prediction mode                is applied on the chroma component and the linear                interpolation thereafter can be skipped.            -   iii. In one example, the same ALWIP intra-prediction                mode is applied on the chroma component with a                subsampled matrix and/or bias vector.        -   d. In one example, the number of ALWIP intra-prediction            modes for different component may be different.            -   i. For example, the number of ALWIP intra-prediction                modes for chroma components may be less than that for                luma component for the same block width and height.                Applicability of ALWIP    -   14. It is proposed that whether ALWIP can be applied may be        signaled.        -   a. For example, it may be signaled at sequence level (e.g.            in SPS), at picture level (e.g. in PPS or picture header),            at slice level (e.g. in slice header), at tile group level            (e.g. in tile group header), at tile level, at CTU row            level, or at CTU level.        -   b. For example, intra_lwip_flag may not be signaled and            inferred to be 0 if ALWIP cannot be applied.    -   15. It is proposed that whether ALWIP can be applied may depend        on the block width (W) and/or height (H).        -   c. For example, ALWIP may not be applied if W>=T1 (or W>T1)            and H>=T2 (or H>T2). E.g. T1=T2=32;            -   i. For example, ALWIP may not be applied if W<=T1 (or                W<T1) and H<=T2 (or H<T2). E.g. T1=T2=32;        -   d. For example, ALWIP may not be applied if W>=T1 (or W>T1)            or H>=T2 (or H>T2). E.g. T1=T2=32;            -   i. For example, ALWIP may not be applied if W<=T1 (or                W<T1) or H<=T2 (or H<T2). E.g. T1=T2=32, or T1=T2=8;        -   e. For example, ALWIP may not be applied if W+H>=T (or            W*H>T). E.g. T=256;            -   i. For example, ALWIP may not be applied if W+H<=T (or                W+H<T). E.g. T=256;        -   f. For example, ALWIP may not be applied if W*H>=T (or            W*H>T). E.g. T=256;            -   i. For example, ALWIP may not be applied if W*H<=T (or                W*H<T). E.g. T=256;        -   g. For example, intra_lwip_flag may not be signaled and            inferred to be 0 if ALWIP cannot be applied.            Calculation Problems in ALWIP    -   16. It is proposed that any shift operation involved in ALWIP        can only left shift or right shift a number by S, where S must        be larger or equal to 0.        -   a. In one example, the right shift operation may be            different when S is equal to 0 or larger than 0.            -   i. In one example, upsBdryX[x] should be calculated as                upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i]+(1<<(Log                2(uDwn)−1)))>>Log 2(uDwn) when uDwn>1, and                upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i] when uDwn                is equal to 1.        -   b. In one example, upsBdryX[x] should be calculated as            upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i]+(1<<Log            2(uDwn)>>1))>>Log 2(uDwn)    -   17. It is proposed that the results should be rounded        toward-zero or away-from-zero in the up-sampling process of        ALWIP.        -   a. In one example,            predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor  (8-X39)            and            predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer  (8-X40)    -   where offsetHor and offsetVer are integers. For example,        offsetHor=upHor/2 and offsetVer=upVer/2.        Interaction with Other Coding Tools    -   18. It is proposed that ALWIP may be used for a CIIP-coded        block.        -   a. In one example, in a CIIP-coded block, it may be            explicitly signaled whether an ALWIP intra-prediction mode            or a normal intra prediction mode such as Planar is used to            generate the intra prediction signal.        -   b. In one example, it may be implicitly inferred whether an            ALWIP intra-prediction mode or a normal intra prediction            mode such as Planar may be used to generate the intra            prediction signal.            -   i. In one example, ALWIP intra-prediction mode may never                be used in a CIIP coded block.                -   1) Alternatively, normal intra prediction may never                    be used in a CIIP coded block.            -   ii. In one example, it may be inferred from information                of neighboring blocks whether an ALWIP intra-prediction                mode or a normal intra prediction mode such as Planar is                used to generate the intra prediction signal.    -   19. It is proposed that the whole or partial of the procedure        used to down-sample the neighboring luma samples in the CCLM        mode may be used to down-sample the neighboring samples in the        ALWIP mode.        -   a. Alternatively, the whole or partial of the procedure used            to down-sample the neighboring luma samples in the ALWIP            mode may be used to down-sample the neighboring samples in            the CCLM mode.        -   b. The down-sampling procedure may be invoked with different            parameters/arguments when it is used in the CCLM process and            ALWIP process.        -   c. In one example, the down-sampling method (such as            selection of neighboring luma locations, down-sampling            filters) in the CCLM process may be utilized in the ALWIP            process.        -   d. The procedure used to down-sample the neighboring luma            samples at least include the selection of down-sampled            positions, the down-sampling filters, the rounding and            clipping operations.    -   20. It is proposed that a block coded with ALWIP mode cannot        apply RST or/and secondary transform or/and rotation transform        or/and Non-Separable Secondary Transform (NSST).        -   a. In one example, whether such constraint may be applied or            not may depend on the dimension information of the block,            e.g., same as conditions described in (15).        -   b. Alternatively, ALWIP mode may be disallowed when RST            or/and secondary transform or/and rotation transform or/and            NSST is applied.        -   c. Alternatively, a block coded with ALWIP mode may apply            RST or/and secondary transform or/and rotation transform            or/and Non-Separable Secondary Transform (NSST).            -   i. In one example, the selection of transform matrix may                depend the ALWIP intra-prediction mode.            -   ii. In one example, the selection of transform matrix                may depend the normal intra-prediction mode which is                converted from the ALWIP intra-prediction mode.            -   iii. In one example, the selection of transform matrix                may depend the classification on the normal                intra-prediction mode which is converted from the ALWIP                intra-prediction mode.    -   21. It is proposed that a block coded with ALWIP mode cannot        apply Block-based DPCM (BDPCM) or Residue RDPCM.        -   a. Alternatively, ALWIP mode may be disallowed when BDPCM or            RDPCM is applied.    -   22. It is proposed that a block coded with ALWIP mode may only        use DCT-II as the transform.        -   a. In one example, the signalling of transform matrix            indices is always skipped.        -   b. Alternatively, it is proposed that the transform used for            a block coded with ALWIP mode may be implicitly derived            instead of explicitly signaled. For example, the transform            may be selected following the way proposed in JVET-M0303.        -   c. Alternatively, it is proposed that a block coded with            ALWIP mode may only use transform skip.            -   i. Alternatively, furthermore, when ALWIP is used, the                signalling of indication of usage of transform skip is                skipped.        -   d. In one example, ALWIP mode information (such as            enabled/disabled, prediction mode index) may be            conditionally signalled after indications of transform            matrix.            -   i. In one example, for a given transform matrix (such as                transform skip or DCT-II), the indications of ALWIP mode                information may be signalled.            -   ii. Alternatively, furthermore, the indications of ALWIP                mode information may be skipped for some pre-defined                transform matrices.    -   23. It is proposed that a block coded with ALWIP mode is        regarded to be coded with a normal intra-prediction converted        from the ALWIP intra-prediction mode when the selected transform        is mode-dependent.    -   24. ALWIP mode may not use transform skip.        -   a. For example, there is no need to further signal the            indication of usage of transform skip in this case.        -   b. Alternatively, ALWIP mode may be disallowed when            transform skip is applied.            -   i. For example, there is no need to signal ALWIP mode                information when transform skip is applied in this case.    -   25. In the filtering process, such as deblocking filter, sample        adaptive offset (SAO), adaptive loop filter (ALF), how to select        the filters and/or whether to filter samples may be determined        by the usage of ALWIP.    -   26. Unfiltered neighboring samples may be used in ALWIP mode.        -   a. Alternatively, filtered neighboring samples may be used            in ALWIP mode.        -   b. In one example, filtered neighboring samples may be used            for down sampling and unfiltered neighboring samples may be            used for up sampling.        -   c. In one example, unfiltered neighboring samples may be            used for down sampling and filtered neighboring samples may            be used for up sampling.        -   d. In one example, filtered left neighboring samples may be            used in up sampling and unfiltered above neighboring samples            may be used in up sampling.        -   e. In one example, unfiltered left neighboring samples may            be used in up sampling and filtered above neighboring            samples may be used in up sampling.        -   f. In one example, whether filter or unfiltered neighboring            samples is used may depend on the ALWIP mode.            -   i. In one example, ALWIP mode may be converted to                traditional intra prediction mode, and whether filtered                or unfiltered neighboring samples is used may depend on                the converted traditional intra prediction mode. For                example, such decision is same as traditional intra                prediction modes.            -   ii. Alternatively, whether filter or unfiltered                neighboring samples is used for ALWIP mode may be                signaled.        -   g. In one example, the filtered samples may be generated            same as traditional intra prediction modes.    -   27. Which matrices or/and offset vectors are used may depend on        reshaping (a.k.a. LMCS, luma mapping with chroma scaling)        information.        -   a. In one example, different matrices or/and offset vectors            may be used when reshaping is on and off.        -   b. In one example, different matrices or/and offset vectors            may be used for different reshaping parameters.        -   c. In one example, ALWIP may be always performed in original            domain.            -   i. For example, neighboring sample are mapped to the                original domain (if reshaping is applied) before used in                ALWIP.    -   28. ALWIP may be disabled when reshaping is applied.        -   a. Alternatively, reshaping may be disabled when ALWIP is            enabled.        -   b. In one example, ALWIP may be disabled for HDR (high            dynamic range) content when reshaping is applied.    -   29. The matrices used in ALWIP may depend on sample bit-depth.    -   30. It is proposed that the prediction generated by ALWIP may be        treated as an intermediate signal which will be processed to        obtain the prediction signal to be further used.        -   a. In one example, Position Dependent Intra Prediction            Combination (PDPC) may be applied on the prediction            generated by ALWIP to generate the prediction signal to be            further used.        -   b. In one example, the boundary samples prediction generated            by ALWIP may be filtered with neighbouring samples to            generate the prediction signal to be further used.    -   31. It is proposed that interpolation filters other than        bilinear interpolation filter may be used in the up-sampling        process of ALWIP.        -   a. In one example, 4-tap interpolation filters may be used            in the up-sampling process of ALWIP.            -   i. For example, the 4-tap interpolation filters in VVC                used to do the motion compensation for chroma components                may be used in the up-sampling process of ALWIP.            -   ii. For example, the 4-tap interpolation filters in VVC                used to do angular intra-prediction may be used in the                up-sampling process of ALWIP.            -   iii. For example, the 8-tap interpolation filters in VVC                used to do the motion compensation for luma component                may be used in the up-sampling process of ALWIP.

The examples described above may be incorporated in the context of themethods described below, e.g., methods 1100 to 1400, and 2000 to 3800,which may be implemented at a video encoder and/or decoder.

FIG. 11 shows a flowchart of an exemplary method for video processing.The method 1100 includes, at step 1102, determining that a current videoblock is coded using an affine linear weighted intra prediction (ALWIP)mode.

The method 1100 includes, at step 1104, constructing, based on thedetermining, at least a portion of a most probable mode (MPM) list forthe ALWIP mode based on an at least a portion of an MPM list for anon-ALWIP intra mode.

The method 1100 includes, at step 1106, performing, based on the MPMlist for the ALWIP mode, a conversion between the current video blockand a bitstream representation of the current video block.

In some embodiments, a size of the MPM list of the ALWIP mode isidentical to a size of the MPM list for the non-ALWIP intra mode. In anexample, the size of the MPM list of the ALWIP mode is 6.

In some embodiments, the method 1100 further comprises the step ofinserting default modes to the MPM list for the ALWIP mode. In anexample, the default modes are inserted prior to the portion of a MPMlist for the ALWIP mode that is based on the MPM list for the non-ALWIPintra mode. In another example, the default modes are insertedsubsequent to the portion of a MPM list for the ALWIP mode that is basedon the MPM list for the non-ALWIP intra mode. In yet another example,the default modes are inserted in an interleaved manner with the portionof a MPM list for the ALWIP mode that is based on the MPM list for thenon-ALWIP intra mode.

In some embodiments, constructing the MPM list for the ALWIP mode andthe MPM list for the non-ALWIP intra mode is based on one or moreneighboring blocks.

In some embodiments, constructing the MPM list for the ALWIP mode andthe MPM list for the non-ALWIP intra mode is based a height or a widthof the current video block.

In some embodiments, constructing the MPM list for the ALWIP mode isbased on a first set of parameters that is different from a second setof parameters used to construct the MPM list for the non-ALWIP intramode.

In some embodiments, the method 1100 further includes the step ofdetermining that a neighboring block of the current video block has beencoded with the ALWIP mode, and designating, in constructing the MPM listfor the non-ALWIP intra mode, the neighboring block as unavailable.

In some embodiments, the method 1100 further includes the step ofdetermining that a neighboring block of the current video block has beencoded with the non-ALWIP intra mode, and designating, in constructingthe MPM list for the ALWIP mode, the neighboring block as unavailable.

In some embodiments, the non-ALWIP intra mode is based on a normal intramode, a multiple reference line (MRL) intra prediction mode or an intrasub-partition (ISP) tool.

FIG. 12 shows a flowchart of an exemplary method for video processing.The method 1200 includes, at step 1210, determining that a lumacomponent of a current video block is coded using an affine linearweighted intra prediction (ALWIP) mode.

The method 1200 includes, at step 1220, inferring, based on thedetermining, a chroma intra mode.

The method 1200 includes, at step 1230, performing, based on the chromaintra mode, a conversion between the current video block and a bitstreamrepresentation of the current video block.

In some embodiments, the luma component covers a predetermined chromasample of the chroma component. In an example, the predetermined chromasample is a top-left sample or a center sample of the chroma component.

In some embodiments, the inferred chroma intra mode is a DM mode.

In some embodiments, the inferred chroma intra mode is the ALWIP mode.

In some embodiments, the ALWIP mode is applied to one or more chromacomponents of the current video block.

In some embodiments, different matrix or bias vectors of the ALWIP modeare applied to different color components of the current video block. Inan example, the different matrix or bias vectors are predefined jointlyfor Cb and Cr components. In another example, the Cb and Cr componentsare concatenated. In yet another example, the Cb and Cr components areinterleaved.

FIG. 13 shows a flowchart of an exemplary method for video processing.The method 1300 includes, at step 1302, determining that a current videoblock is coded using an affine linear weighted intra prediction (ALWIP)mode.

The method 1300 includes, at step 1304, performing, based on thedetermining, a conversion between the current video block and abitstream representation of the current video block.

In some embodiments, the determining is based on signaling in a sequenceparameter set (SPS), a picture parameter set (PPS), a slice header, atile group header, a tile header, a coding tree unit (CTU) row or a CTUregion.

In some embodiments, the determining is based on a height (H) or a width(W) of the current video block. In an example, W>T1 or H>T2. In anotherexample, W≥T1 or H≥T2. In yet another example, W<T1 or H<T2. In yetanother example, W≤T1 or H≤T2. In yet another example, T1=32 and T2=32.

In some embodiments, the determining is based on a height (H) or a width(W) of the current video block. In an example, W+H≤T. In anotherexample, W+H≥T. In yet another example, W×H≤T. In yet another example,W×H≥T. In yet another example, T=256.

FIG. 14 shows a flowchart of an exemplary method for video processing.The method 1400 includes, at step 1402, determining that a current videoblock is coded using a coding mode different from an affine linearweighted intra prediction (ALWIP) mode.

The method 1400 includes, at step 1404, performing, based on thedetermining, a conversion between the current video block and abitstream representation of the current video block.

In some embodiments, the coding mode is a combined intra and interprediction (CIIP) mode, and method 1400 further includes the step ofperforming a selection between the ALWIP mode and a normal intraprediction mode. In an example, performing the selection is based on anexplicit signaling in the bitstream representation of the current videoblock. In another example, performing the selection is based onpredetermined rule. In yet another example, the predetermined rulealways selects the ALWIP mode when the current video block is codedusing the CIIP mode. In yet another example, the predetermined rulealways selects the normal intra prediction mode when the current videoblock is coded using the CIIP mode.

In some embodiments, the coding mode is a cross-component linear model(CCLM) prediction mode. In an example, a downsampling procedure for theALWIP mode is based on a downsampling procedure for the CCLM predictionmode. In another example, the downsampling procedure for the ALWIP modeis based on a first set of parameters, and where the downsamplingprocedure for the CCLM prediction mode is based on a second set ofparameters different from the first set of parameters. In yet anotherexample, the downsampling procedure for the ALWIP mode or the CCLMprediction mode comprises at least one of a selection of downsampledpositions, a selection of downsampling filters, a rounding operation ora clipping operation.

In some embodiments, the method 1400 further includes the step ofapplying one or more of a Reduced Secondary Transform (RST), a secondarytransform, a rotation transform or a Non-Separable Secondary Transform(NSST).

In some embodiments, the method 1400 further includes the step ofapplying block-based differential pulse coded modulation (DPCM) orresidual DPCM.

6 Example Implementations of the Disclosed Technology

FIG. 15 is a block diagram of a video processing apparatus 1500. Theapparatus 1500 may be used to implement one or more of the methodsdescribed herein. The apparatus 1500 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 1500 may include one or more processors 1502, one or morememories 1504 and video processing hardware 1506. The processor(s) 1502may be configured to implement one or more methods (including, but notlimited to, methods 1100 to 1400, and 2000 to 3800) described in thepresent document. The memory (memories) 1504 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 1506 may be used to implement, inhardware circuitry, some techniques described in the present document.

In some embodiments, the video coding methods may be implemented usingan apparatus that is implemented on a hardware platform as describedwith respect to FIG. 15.

FIG. 16 is a block diagram showing an example video processing system1600 in which various techniques disclosed herein may be implemented.Various implementations may include some or all of the components of thesystem 1600. The system 1600 may include input 1602 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 1602 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 1600 may include a coding component 1604 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 1604 may reduce the average bitrate ofvideo from the input 1602 to the output of the coding component 1604 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 1604 may be eitherstored, or transmitted via a communication connected, as represented bythe component 1606. The stored or communicated bitstream (or coded)representation of the video received at the input 1602 may be used bythe component 1608 for generating pixel values or displayable video thatis sent to a display interface 1610. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include SATA (serial advanced technology attachment), PCI,IDE interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

Some embodiments of the disclosed technology include making a decisionor determination to enable a video processing tool or mode. In anexample, when the video processing tool or mode is enabled, the encoderwill use or implement the tool or mode in the processing of a block ofvideo, but may not necessarily modify the resulting bitstream based onthe usage of the tool or mode. That is, a conversion from the block ofvideo to the bitstream representation of the video will use the videoprocessing tool or mode when it is enabled based on the decision ordetermination. In another example, when the video processing tool ormode is enabled, the decoder will process the bitstream with theknowledge that the bitstream has been modified based on the videoprocessing tool or mode. That is, a conversion from the bitstreamrepresentation of the video to the block of video will be performedusing the video processing tool or mode that was enabled based on thedecision or determination.

Some embodiments of the disclosed technology include making a decisionor determination to disable a video processing tool or mode. In anexample, when the video processing tool or mode is disabled, the encoderwill not use the tool or mode in the conversion of the block of video tothe bitstream representation of the video. In another example, when thevideo processing tool or mode is disabled, the decoder will process thebitstream with the knowledge that the bitstream has not been modifiedusing the video processing tool or mode that was disabled based on thedecision or determination.

FIG. 17 is a block diagram that illustrates an example video codingsystem 100 that may utilize the techniques of this disclosure. As shownin FIG. 17, video coding system 100 may include a source device 110 anda destination device 120. Source device 110 generates encoded video datawhich may be referred to as a video encoding device. Destination device120 may decode the encoded video data generated by source device 110which may be referred to as a video decoding device. Source device 110may include a video source 112, a video encoder 114, and an input/output(I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130 bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard, Versatile Video Coding (VVM) standard and other current and/orfurther standards.

FIG. 18 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 17.

Video encoder 200 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 18, video encoder200 includes a plurality of functional components. The techniquesdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a predication unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205 and anintra prediction unit 206, a residual generation unit 207, a transformunit 208, a quantization unit 209, an inverse quantization unit 210, aninverse transform unit 211, a reconstruction unit 212, a buffer 213, andan entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, predication unit 202 mayinclude an intra block copy (IBC) unit. The IBC unit may performpredication in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated but arerepresented in the example of FIG. 18 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some example, Mode select unit203 may select a combination of intra and inter predication (CIIP) modein which the predication is based on an inter predication signal and anintra predication signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the current video block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block of the current video block based on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a fullset of motion information for the current video. Rather, motionestimation unit 204 may signal the motion information of the currentvideo block with reference to the motion information of another videoblock. For example, motion estimation unit 204 may determine that themotion information of the current video block is sufficiently similar tothe motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as another video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signaling techniques that may beimplemented by video encoder 200 include advanced motion vectorpredication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the predication unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed reduce video blocking artifacts inthe video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encoding unit 214receives the data, entropy encoding unit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 19 is a block diagram illustrating an example of video decoder 300which may be video decoder 114 in the system 100 illustrated in FIG. 17.

The video decoder 300 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 19, the videodecoder 300 includes a plurality of functional components. Thetechniques described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the techniques described in thisdisclosure.

In the example of FIG. 19, video decoder 300 includes an entropydecoding unit 301, a motion compensation unit 302, an intra predictionunit 303, an inverse quantization unit 304, an inverse transformationunit 305, and a reconstruction unit 306 and a buffer 307. Video decoder300 may, in some examples, perform a decoding pass generally reciprocalto the encoding pass described with respect to video encoder 200 (FIG.18).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit 302 may determine motion information including motion vectors,motion vector precision, reference picture list indexes, and othermotion information. Motion compensation unit 302 may, for example,determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 20 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may uses some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent blocks. Inverse quantization unit 303 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit202 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decoded video blocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation/intra predication and also produces decoded videofor presentation on a display device.

In some embodiments, the ALWIP mode or the MIP mode is used to compute aprediction block of the current video block by performing, on previouslycoded samples of the video, a boundary downsampling operation (or anaveraging operation), followed by a matrix vector multiplicationoperation, and selectively (or optionally) followed by an upsamplingoperation (or a linear interpolation operation). In some embodiments,the ALWIP mode or the MIP mode is used to compute a prediction block ofthe current video block by performing, on previously coded samples ofthe video, a boundary downsampling operation (or an averaging operation)and followed by a matrix vector multiplication operation. In someembodiments, the ALWIP mode or the MIP mode can also perform anupsampling operation (or a linear interpolation operation) afterperforming the matrix vector multiplication operation.

FIG. 20 shows an example flowchart of an example method 2000 formatrix-based intra prediction. Operation 2002 includes generating, for aconversion between a current video block of a video and a codedrepresentation of the current video block, a first most probable mode(MPM) list using a first procedure based on a rule. Operation 2004includes performing the conversion between the current video block andthe coded representation of the current video block using the first MPMlist, where the conversion of the current video block uses a matrixbased intra prediction (MIP) mode in which a prediction block of thecurrent video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation, where the rule specifies that the first procedureused for generation of the first MPM list is same as a second procedureused for generation of a second MPM list for conversion of other videoblocks of the video that are coded using a non-MIP intra mode that isdifferent from the MIP mode, and where at least a portion of the firstMPM list is generated based on at least a portion of the second MPMlist.

In some embodiments for method 2000, a size of the first MPM list forthe MIP mode is same as that of the second MPM list for the non-MIPintra mode. In some embodiments for method 2000, the size of the firstMPM list for the MIP mode and of the second MPM list for the non-MIPintra mode is 6. In some embodiments for method 2000, the second MPMlist for the non-MIP intra mode is constructed before the first MPM listfor the MIP mode is constructed. In some embodiments for method 2000,the portion or all of the second MPM list for the non-MIP intra mode isconverted to MPMs that are added to the portion of the first MPM listfor the MIP mode.

In some embodiments for method 2000, a subset of the MPMs are added tothe portion of the first MPM list for the MIP mode by pruning the MPMs.In some embodiments, the method 2000 further includes adding defaultintra-prediction modes to the first MPM list for the MIP mode. In someembodiments for method 2000, the default intra-prediction modes areadded to the first MPM list for the MIP mode prior to the portion of thefirst MPM list for the MIP mode that is based on the portion of thesecond MPM list for the non-MIP intra mode. In some embodiments formethod 2000, the default intra-prediction modes are added to the firstMPM list for the MIP mode after the portion of the first MPM list forthe MIP mode that is based on the portion of the second MPM list for thenon-MIP intra mode. In some embodiments for method 2000, the defaultintra-prediction modes are added to the first MPM list for the MIP modein an interleaved manner with the portion of the first MPM list for theMIP mode that is based on the portion of the second MPM list for thenon-MIP intra mode. In some embodiments for method 2000, the defaultintra-prediction modes are same for a plurality of types of videoblocks. In some embodiments for method 2000, the defaultintra-prediction modes are determined based on coded information of thecurrent video block. In some embodiments for method 2000, the codedinformation includes availability of neighboring video blocks, modeinformation of the neighboring video blocks, or block dimension of thecurrent video block.

In some embodiments for method 2000, one intra-prediction mode in thesecond MPM list for the non-MIP intra mode is converted to itscorresponding MIP mode to obtain a converted MIP mode that is added tothe first MPM list for the MIP mode. In some embodiments for method2000, all intra-prediction modes in the second MPM list for the non-MIPintra mode are converted to its corresponding MIP mode to obtain aplurality of converted MIP modes that are added to the first MPM listfor the MIP mode. In some embodiments for method 2000, allintra-prediction modes are converted to its corresponding MIP mode toobtain a plurality of converted MIP modes that are used to construct thesecond MPM list for the non-MIP intra mode. In some embodiments formethod 2000, the all intra-prediction modes include intra-predictionmodes from neighboring video blocks of the current video block anddefault intra-prediction modes. In some embodiments for method 2000, thedefault intra-prediction modes include a planar mode and a directcurrent (DC) mode.

In some embodiments for method 2000, two intra-prediction modes in thesecond MPM list for the non-MIP intra mode are converted to itscorresponding MIP modes to obtain two converted MIP modes, and one oftwo converted MIP modes is added to the first MPM list for the MIP modein response to the two converted MIP modes being same. In someembodiments for method 2000, two intra-prediction modes in the secondMPM list for the non-MIP intra mode are converted to its correspondingMIP modes to obtain two converted MIP modes, and one of two convertedMIP modes is added to the second MPM list for the non-MIP intra mode inresponse to the two converted MIP modes being same. In some embodimentsfor method 2000, the second MPM list for non-MIP intra mode includes Sintra-prediction modes, and where K out of S intra-prediction modes isor are selected to be included in the first MPM list for MIP mode. Insome embodiments for method 2000, K is 3 and S is 6. In some embodimentsfor method 2000, the first K intra-prediction modes in the second MPMlist for non-MIP intra mode is selected to be included in the first MPMlist for MIP mode. In some embodiments for method 2000, the first MPMlist for the MIP mode and the second MPM list for the non-MIP intra modeis derived or constructed based on one or more neighboring video blocksof the current video block. In some embodiments for method 2000, thefirst MPM list for the MIP mode and the second MPM list for the non-MIPintra mode is derived or constructed based on a same neighboring videoblock located to a left of the current video block.

In some embodiments for method 2000, the same neighboring video blocklocated to the left is directly to left of the current video block andis aligned with the current video block. In some embodiments for method2000, the same neighboring video block located to the left and below thecurrent video block. In some embodiments for method 2000, the first MPMlist for the MIP mode and the second MPM list for the non-MIP intra modeis derived or constructed based on a same neighboring video block, wherethe same neighboring video block is located to left of the current videoblock at a bottom-most position or the same neighboring video block islocated above the current video block at a right-most position. In someembodiments for method 2000, the first MPM list for the MIP mode and thesecond MPM list for the non-MIP intra mode is derived or constructedbased on a same neighboring video block located above the current videoblock.

In some embodiments for method 2000, the same neighboring video blocklocated to above is directly above the current video block and isaligned with the current video block. In some embodiments for method2000, the same neighboring video block located to left and above thecurrent video block. In some embodiments for method 2000, the first MPMlist for the MIP mode and the second MPM list for the non-MIP intra modeis derived or constructed based on a same neighboring video block, wherethe same neighboring video block is located above the current videoblock at a left-most position or the same neighboring video block islocated to left of the current video block at a top-most position. Insome embodiments for method 2000, the non-MIP intra mode is based on anintra prediction mode, a multiple reference line (MRL) intra predictionmode, or an intra sub-partition (ISP) tool. In some embodiments formethod 2000, the first MPM list for the MIP mode is further based on aheight or a width of the current video block.

In some embodiments for method 2000, the first MPM list for the MIP modeis further based on a height or a width of a neighboring video block ofthe current video block. In some embodiments for method 2000, the firstMPM list for the MIP mode is constructed based on a first set ofparameters that is different from a second set of parameters used toconstruct the second MPM list for the non-MIP intra mode. In someembodiments for method 2000, the second MPM list for non-MIP intra modeincludes S intra-prediction modes, and where K out of S intra-predictionmodes are derived to be included in the first MPM list for MIP mode. Insome embodiments for method 2000, K is 3 and S is 6.

In some embodiments for method 2000, the first K intra-prediction modesin the second MPM list for non-MIP intra mode is derived to be includedin the first MPM list for MIP mode. In some embodiments for method 2000,a first mode listed in the first MPM list for MIP mode is different froma first mode listed in the second MPM list for non-MIP intra mode. Insome embodiments for method 2000, the first mode listed in the first MPMlist for MIP mode is a first mode, and where the first mode listed inthe second MPM list for non-MIP intra mode is a planar mode. In someembodiments for method 2000, the first mode in the first MPM list forMIP mode is converted from the planar mode in the second MPM list fornon-MIP intra mode.

In some embodiments for method 2000, the first MPM list for MIP modeincludes a first set of stuffing modes that are different from a secondset of stuffing modes included in the second MPM list for non-MIP intramode. In some embodiments for method 2000, the first set of stuffingmodes include a first mode, a second mode, and a third mode, and wherethe second set of stuffing modes include a direct current (DC) mode, avertical mode, and a horizontal mode. In some embodiments for method2000, the first mode, the second mode, and the third mode are includedin the first set of stuffing modes based on a size of the current videoblock. In some embodiments for method 2000, the first MPM list for MIPmode includes a first set of intra-prediction modes of neighboring videoblocks of the current video block, the second MPM list for non-MIP intramode includes a second set of intra-prediction modes of the neighboringvideo blocks of the current video block, and the first set ofintra-prediction modes are different from the second set ofintra-prediction modes.

In some embodiments for method 2000, the second set of intra-predictionmodes include intra-prediction modes that are converted to MIP modesthat are included in the first set of intra-prediction modes. In someembodiments for method 2000, the first MPM list for MIP mode includes afirst set of shifted intra-prediction modes, the second MPM list fornon-MIP intra mode includes a second set of shifted intra-predictionmodes, and the first set of shifted intra-prediction modes are differentfrom the second set of shifted intra-prediction modes. In someembodiments for method 2000, the first set of shifted intra-predictionmodes includes an MIP mode (Y) shifted by K1 according to a firstformula Y+K1, the second set of shifted intra-prediction modes includesa non-MIP intra mode (X) shifted by K0 according to a second formulaX+K0, and K1 is different from K0. In some embodiments for method 2000,K1 depends on a width and a height of the current video block.

In some embodiments, the method 2000 further includes performing a firstdetermination that a neighboring video block of the current video blockis coded with a non-MIP intra mode; and performing a seconddetermination, in response to the first determination, that theneighboring video block is unavailable for the constructing of the firstMPM list for the MIP mode.

In some embodiments, the method 2000 further includes performing a firstdetermination that a neighboring video block of the current video blockis coded with a non-MIP intra mode; and performing, in response to thefirst determination, a second determination that the neighboring videoblock is coded with a pre-defined MIP intra-prediction mode, where thefirst MPM list for the MIP mode is constructed using the pre-defined MIPintra-prediction mode. In some embodiments for method 2000, thepre-defined MIP intra-prediction mode depends on a width and/or a heightof the current video block.

FIG. 21 shows an example flowchart of an example method 2100 formatrix-based intra prediction. Operation 2100 includes generating, for aconversion between a current video block of a video and a codedrepresentation of the current video block, a most probable mode (MPM)list based on a rule, where the rule is based on whether a neighboringvideo block of the current video block is coded with a matrix basedintra prediction (MIP) mode in which a prediction block of theneighboring video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation. Operation 2104 includes performing the conversionbetween the current video block and the coded representation of thecurrent video block using the MPM list, where the conversion applies anon-MIP mode to the current video block, and where the non-MIP mode isdifferent from the MIP mode.

In some embodiments for method 2100, the rule specifies that theneighboring video block coded with the MIP mode is treated asunavailable for generating the MPM list for the non-MIP coded currentvideo block. In some embodiments for method 2100, the rule specifiesthat the neighboring video block coded with the MIP mode is determinedto be coded with a pre-defined intra-prediction mode. In someembodiments for method 2100, the rule specifies that the pre-definedintra-prediction mode includes a planar mode.

FIG. 22 shows an example flowchart of an example method 2200 formatrix-based intra prediction. Operation 2202 includes decoding acurrent video block of a video that is coded in a coded representationof the current video block using a matrix based intra prediction (MIP)mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 2204 includes updating a line buffer associatedwith the decoding without storing in the line buffer informationindicating whether the current video block is coded using the MIP mode.

In some embodiments, the method 2200 further includes accessing a secondvideo block of the video, where the second video block is decoded beforethe decoding the current video block, where the second video block islocated at a different Largest Coding Unit (LCU) or Coding Tree Unit(CTU) row or CTU region compared to that of the current video block, andwhere the current video block is decoded without determining whether thesecond video block is coded using the MIP mode. In some embodiments, themethod 2200 further includes accessing a second video block bydetermining that the second video block is coded using a non-MIP intramode without determining whether the second video block is coded usingthe MIP mode, where the second video located at a different LargestCoding Unit (LCU) or Coding Tree Unit (CTU) row or CTU region comparedto that of the current video block; and decoding, based on the accessingthe second video block, the current video block.

FIG. 23 shows an example flowchart of an example method 2300 formatrix-based intra prediction. Operation 2302 includes performing aconversion between a current video block and a bitstream representationof the current video block, where the current video block is coded usinga matrix based intra prediction (MIP) mode in which a prediction blockof the current video block is determined by performing, on previouslycoded samples of the video, a boundary downsampling operation, followedby a matrix vector multiplication operation, and selectively followed byan upsampling operation, where a flag is coded in the bitstreampresentation using at most K contexts in an arithmetic coding or adecoding process, where the flag indicates whether the current videoblock is coded using the MIP mode, and where K is greater than or equalto zero. In some embodiments for method 2300, K is 1. In someembodiments for method 2300, K is 4.

FIG. 24 shows an example flowchart of an example method 2400 formatrix-based intra prediction. Operation 2402 includes generating, for aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, an intra prediction mode forthe current video block coded with a matrix based intra prediction (MIP)mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 2404 includes determining a rule for storinginformation indicative of the intra prediction mode based on whether thecurrent video block is coded with the MIP mode. Operation 2406 includesperforming the conversion according to the rule, where the rule definesthat a syntax element for the intra prediction mode is stored in thebitstream representation for the current video block, and where the ruledefines that a mode index for the MIP mode for the current video blockis not stored in the bitstream representation.

In some embodiments for method 2400, the mode index for the MIP mode isassociated with the intra prediction mode. In some embodiments formethod 2400, the rule defines that the bitstream representation excludesa flag that indicates that the current video block is coded with the MIPmode. In some embodiments for method 2400, the rule defines that thebitstream representation excludes a storage of information indicative ofthe MIP mode associated with the current video block. In someembodiments, the method 2400 further includes performing, after theconversion, a second conversion between a second video block of thevideo and the bitstream representation of the second video block, wherethe second video block is a neighboring video block of the current videoblock, and where the second conversion is performed without determiningwhether the second video block is coded using the MIP mode.

FIG. 25 shows an example flowchart of an example method 2500 formatrix-based intra prediction. Operation 2502 includes performing afirst determination that a luma video block of a video is coded using amatrix based intra prediction (MIP) mode in which a prediction block ofthe luma video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation. Operation 2504 includes performing, based on thefirst determination, a second determination about a chroma intra mode tobe used for a chroma video block associated with the luma video block.Operation 2506 includes performing, based on the second determination, aconversion between the chroma video block and a bitstream representationof the chroma video block.

In some embodiments for method 2500, the performing the seconddetermination includes determining that the chroma intra mode is aDerived Mode (DM) without depending on a signaling. In some embodimentsfor method 2500, the luma video block covers a predeterminedcorresponding chroma sample of the chroma video block. In someembodiments for method 2500, the predetermined corresponding chromasample is a top-left sample or a center sample of the chroma videoblock. In some embodiments for method 2500, the chroma intra modeincludes a Derived Mode (DM). In some embodiments for method 2500, theDM is used to derive a first intra prediction mode for the chroma videoblock from a second intra prediction mode of the luma video block. Insome embodiments for method 2500, the MIP mode associated with the lumavideo block is mapped to a pre-defined intra mode.

In some embodiments for method 2500, a plurality of Derived Modes (DMs)are derived in response to the first determination that the luma videoblock is coded with the MIP mode. In some embodiments for method 2500,the chroma intra mode includes a specified intra prediction mode. Insome embodiments for method 2500, the pre-defined intra mode or thespecified intra mode is a Planar mode. In some embodiments for method2500, the chroma video block is coded using the MIP mode. In someembodiments for method 2500, the chroma video block is coded using afirst matrix or a first bias vector that are different from a secondmatrix or a second bias vector of a second chroma video block. In someembodiments for method 2500, the chroma video block is a blue colorcomponent, where the first matrix or the first bias vector is predefinedfor the blue color component, where the second chroma video block is ared color component, where the second matrix or the second bias vectoris predefined for the red color component.

In some embodiments for method 2500, the blue color component and thered color component are concatenated. In some embodiments for method2500, the blue color component and the red color component areinterleaved. In some embodiments for method 2500, the chroma video blockis coded using the MIP mode that is same as the MIP mode used for theluma video block. In some embodiments for method 2500, the chroma videoblock is coded using a Derived Mode (DM). In some embodiments for method2500, the upsampling operation (or a linear interpolation technique) isskipped after the chroma video block is coded using the MIP mode. Insome embodiments for method 2500, the chroma video block is coded usingthe MIP mode with a subsampled matrix and/or a bias vector. In someembodiments for method 2500, a number of MIP modes for the luma videoblock and the chroma video block are different. In some embodiments formethod 2500, the chroma video block is associated with a first number ofMIP modes, the luma video block is associated with a second number ofMIP modes, and the first number of MIP modes is less than the secondnumber of MIP modes. In some embodiments for method 2500, the chromavideo block and the luma video block have a same size.

FIG. 26 shows an example flowchart of an example method 2600 formatrix-based intra prediction. Operation 2602 includes performing aconversion between a current video block of a video and a codedrepresentation of the current video block, where the conversion is basedon a determination (or based on determining) whether to code the currentvideo block using a matrix based intra prediction (MIP) mode in which aprediction block of the current video block is determined by performing,on previously coded samples of the video, a boundary downsamplingoperation, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation.

In some embodiments of method 2600, a syntax element is included in thecoded representation in response to the determination that the currentvideo block is to be coded with the MIP mode, and the syntax elementindicates the use the MIP mode for coding the current video block. Insome embodiments of method 2600, the coded representation includes asyntax element that indicates that the MIP mode is enabled or disabledfor the current video block, and where the syntax element indicates thatthe MIP mode is allowed or disallowed for coding the current videoblock. In some embodiments of method 2600, a syntax element is notincluded in the coded representation in response to the determinationthat the current video block is not to be coded with the MIP mode, andthe syntax element indicates whether the MIP mode is used for thecurrent video block.

In some embodiments of method 2600, a second syntax element indicatingenabling of the MIP mode is further included in a sequence parameter set(SPS), a picture parameter set (PPS), a slice header, a tile groupheader, a tile header, a coding tree unit (CTU) row or a CTU region. Insome embodiments of method 2600, the determination whether to use theMIP mode for the conversion is based on a height (H) and/or a width (W)of the current video block. In some embodiments of method 2600, thecurrent video block is determined not to be coded using the MIP mode inresponse to W≥T1 and H≥T2. In some embodiments of method 2600, thecurrent video block is determined not to be coded using the MIP mode inresponse to W≤T1 and H≤T2. In some embodiments of method 2600, thecurrent video block is determined not to be coded using the MIP mode inresponse to W≥T1 or H≥T2. In some embodiments of method 2600, thecurrent video block is determined not to be coded using the MIP mode inresponse to W≤T1 or H≤T2. In some embodiments of method 2600, T1=32 andT2=32. In some embodiments of method 2600, the current video block isdetermined not to be coded using the MIP mode in response to W+H≥T. Insome embodiments of method 2600, the current video block is determinednot to be coded using the MIP mode in response to W+H≤T. In someembodiments of method 2600, the current video block is determined not tobe coded using the MIP mode in response to W×H≥T. In some embodiments ofmethod 2600, the current video block is determined not to be coded usingthe MIP mode in response to W×H≤T. In some embodiments of method 2600,T=256.

FIG. 27A shows an example flowchart of an example video encoding method2700A for matrix-based intra prediction. Operation 2702A includesdetermining, for encoding a current video block of a video into abitstream representation of the current video block, according to a rulewhether to use a matrix based intra prediction (MIP) mode and a codingmode that is different from the MIP mode for encoding the current videoblock, where the MIP mode includes determining a prediction block of thecurrent video block by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 2704A includes adding, based on the determining, anencoded representation of the current video block to the bitstreamrepresentation.

FIG. 27B shows an example flowchart of an example video decoding method2700B for matrix-based intra prediction. Operation 2702B includesdetermining that a current video block of a video is encoded in abitstream representation using a matrix based intra prediction (MIP)mode and a coding mode that is different from the MIP mode, where theMIP mode includes determining a prediction block of the current videoblock by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 2704B includes generating a decoded representationof the current video block by parsing and decoding the bitstreamrepresentation.

In some embodiments for methods 2700A and/or 2700B, the coding mode is acombined intra and inter prediction (CIIP) mode, and where the methodfurther comprises generating an intra prediction signal for the currentvideo block by performing a selection between the MIP mode and an intraprediction mode. In some embodiments for methods 2700A and/or 2700B, theperforming the selection is based on a signaling in the bitstreamrepresentation of the current video block. In some embodiments formethods 2700A and/or 2700B, the performing the selection is based on apredetermined rule. In some embodiments for methods 2700A and/or 2700B,the predetermined rule selects the MIP mode in response to the currentvideo block being coded using the CIIP mode. In some embodiments formethods 2700A and/or 2700B, the predetermined rule selects the intraprediction mode in response to the current video block being coded usingthe CIIP mode. In some embodiments for method 2700A and/or 2700B, thepredetermined rule selects a Planar mode in response to the currentvideo block being coded using the CIIP mode. In some embodiments formethods 2700A and/or 2700B, the performing the selection is based oninformation associated with neighboring video blocks of the currentvideo block.

In some embodiments for methods 2700A and/or 2700B, the coding mode is across-component linear model (CCLM) prediction mode. In some embodimentsfor methods 2700A and/or 2700B, a first downsampling procedure fordownsampling a neighboring sample of the current video block in the MIPmode uses at least some of a second downsampling procedure for the CCLMprediction mode in which neighboring luma samples of the current videoblock are downsampled. In some embodiments for methods 2700A and/or2700B, a first downsampling procedure for downsampling a neighboringsample of the current video block in the CCLM prediction mode uses atleast some of a second downsampling procedure for the MIP predictionmode in which neighboring luma samples of the current video block aredownsampled. In some embodiments for methods 2700A and/or 2700B, thefirst downsampling procedure for the MIP mode is based on a first set ofparameters, and the first downsampling procedure for the CCLM predictionmode is based on a second set of parameters different from the first setof parameters.

In some embodiments for methods 2700A and/or 2700B, the firstdownsampling procedure for the MIP mode and the second downsamplingprocedure for the CCLM prediction mode include selection of neighboringluma locations or selection of downsampling filter. In some embodimentsfor methods 2700A and/or 2700B, the neighboring luma samples aredownsampled using at least one of a selection of downsampled positions,a selection of downsampling filters, a rounding operation or a clippingoperation. In some embodiments for methods 2700A and/or 2700B, the ruledefines that a block-based differential pulse coded modulation (BDPCM)or a residual DPCM is not applied to the current video block coded withthe MIP mode. In some embodiments for methods 2700A and/or 2700B, therule defines that the MIP mode is disallowed for applying to the currentvideo block in response to applying a block-based differentialpulse-coded modulation (BDPCM) or a residual DPCM.

FIG. 28 shows an example flowchart of an example method 2800 formatrix-based intra prediction. Operation 2802 includes making adetermination about an applicability of a loop filter to a reconstructedblock of a current video block of a video in a conversion between thevideo and a coded representation of the current video block, where thecurrent video block is coded using a matrix based intra prediction (MIP)mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 2804 includes processing the current video blockaccording to the determination.

In some embodiments for method 2800, the loop filter includes adeblocking filter. In some embodiments for method 2800, the loop filterincludes a sample adaptive offset (SAO). In some embodiments for method2800, the loop filter includes an adaptive loop filter (ALF).

FIG. 29A shows an example flowchart of an example video encoding method2900A for matrix-based intra prediction. Operation 2902A includesdetermining, for encoding a current video block of a video into abitstream representation of the current video block, a type ofneighboring samples of the current video block to be used according to arule. Operation 2904A includes adding, based on the determining, anencoded representation of the current video block to the bitstreamrepresentation, where the current video block is encoded using a matrixbased intra prediction (MIP) mode in which a prediction block of thecurrent video block is determined by performing, on previously codedsamples of the video, a boundary downsampling operation, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation.

FIG. 29B shows an example flowchart of an example video decoding method2900B for matrix-based intra prediction. Operation 2902B includesdetermining that a current video block of a video is encoded in abitstream representation using a matrix based intra prediction (MIP)mode and using a type of neighboring samples of the current video blockaccording to a rule, where the MIP mode includes determining aprediction block of the current video block by performing, on previouslycoded samples of the video, a boundary downsampling operation, followedby a matrix vector multiplication operation, and selectively followed byan upsampling operation. Operation 2904B includes generating a decodedrepresentation of the current video block by parsing and decoding thebitstream representation.

In some embodiments for methods 2900A and/or 2900B, the rule definesthat the type of neighboring samples are unfiltered neighboring samples.In some embodiments for methods 2900A and/or 2900B, the rule definesthat the type of neighboring samples that include the unfilteredneighboring samples are used for an upsampling process, the rule definesthat the type of neighboring samples that include the unfilteredneighboring samples are used for a downsampling process, and the ruledefines that the type of neighboring samples that include the unfilteredneighboring samples are used for the matrix vector multiplicationoperation. In some embodiments for methods 2900A and/or 2900B, the ruledefines that the type of neighboring samples are filtered neighboringsamples. In some embodiments for methods 2900A and/or 2900B, the ruledefines that the type of neighboring samples that include unfilteredneighboring samples are used for an upsampling technique, and the ruledefines that the type of neighboring samples that include filteredneighboring samples are used for a downsampling technique.

In some embodiments for methods 2900A and/or 2900B, the rule definesthat the type of neighboring samples that include unfiltered neighboringsamples are used for a downsampling technique, and the rule defines thatthe type of neighboring samples that include filtered neighboringsamples are used for an upsampling technique. In some embodiments formethods 2900A and/or 2900B, the rule defines that the type ofneighboring samples that include unfiltered above neighboring samplesare used for an upsampling technique, and the rule defines that the typeof neighboring samples that include filtered left neighboring samplesare used for an upsampling technique. In some embodiments for methods2900A and/or 2900B, the rule defines that the type of neighboringsamples that include unfiltered left neighboring samples are used for anupsampling technique, and the rule defines that the type of neighboringsamples that include filtered above neighboring samples are used for anupsampling technique.

In some embodiments for methods 2900A and/or 2900B, the type ofneighboring samples include unfiltered neighboring samples or filteredneighboring samples, and the rule defines that whether the unfilteredneighboring samples or the filtered neighboring samples are used isbased on the MIP mode of the current video block.

In some embodiments, methods 2900A and/or 2900B further compriseconverting the MIP mode to an intra prediction mode, where the type ofneighboring samples include unfiltered neighboring samples or filteredneighboring samples, and where the rule defines that whether theunfiltered neighboring samples or the filtered neighboring samples areused is based on the intra prediction mode. In some embodiments formethods 2900A and/or 2900B, the type of neighboring samples includeunfiltered neighboring samples or filtered neighboring samples, and therule defines that whether the unfiltered neighboring samples or thefiltered neighboring samples are used is based on a syntax element orsignaling. In some embodiments for methods 2900A and/or 2900B, thefiltered neighboring samples or the filtered left neighboring samples orthe filtered above neighboring samples are generated using an intraprediction mode.

FIG. 30 shows an example flowchart of an example method 3000 formatrix-based intra prediction. Operation 3002 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, where the conversion includesgenerating, by using a matrix based intra prediction (MIP) mode, aprediction block for the current video block by selecting and applyingmatrix multiplication using matrices of samples and/or by selecting andadding an offset using offset vectors for the current video block, wherethe samples are obtained from a row and column wise averaging ofpreviously coded samples of the video, and where the selecting is basedon reshaping information associated with applying a luma mapping withchroma scaling (LMCS) technique on a reference picture of the currentvideo block. In some embodiments for method 3000, when a reshapingtechnique is enabled for the reference picture, the reshapinginformation is associated with the matrices and/or the offset vectorsthat are different from those associated with the reshaping informationwhen the reshaping technique is disabled for the reference picture. Insome embodiments for method 3000, different matrices and/or the offsetvectors are used for different reshaping parameters of the reshapinginformation. In some embodiments for method 3000, the performing theconversion includes performing intra prediction on the current videoblock using the MIP mode in an original domain. In some embodiments formethod 3000, neighboring samples of the current video block are mappedto the original domain in response to applying the reshapinginformation, and where the neighboring samples are mapped to theoriginal domain before being used in MIP mode.

FIG. 31 shows an example flowchart of an example method 3100 formatrix-based intra prediction. Operation 3102 includes determining thata current video block is to be coded using a matrix based intraprediction (MIP) mode in which a prediction block of the current videoblock is determined by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 3104 includes performing, based on the determining,a conversion between the current video block and a bitstreamrepresentation of the current video block, where the performing theconversion is based on a rule of co-application of the MIP mode andanother coding technique.

In some embodiments for method 3100, the rule specifies that the MIPmode and the another coding technique are used mutually exclusively. Insome embodiments for method 3100, the rule specifies that the anothercoding technique is high dynamic range (HDR) technique or a reshapingtechnique.

FIG. 32 shows an example flowchart of an example method 3200 formatrix-based intra prediction. Operation 3202 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode, where the performing the conversion using the MIPmode includes generating a prediction block by applying matrixmultiplication using matrices of samples obtained from a row and columnwise averaging of previously coded samples of the video, and where thematrices depend on a bit-depth of a sample.

FIG. 33 shows an example flowchart of an example method 3300 formatrix-based intra prediction. Operation 3302 includes generating, for acurrent video block of a video, an intermediate prediction signal usinga matrix based intra prediction (MIP) mode in which a prediction blockof the current video block is determined by performing, on previouslycoded samples of the video, a boundary downsampling operation, followedby a matrix vector multiplication operation, and selectively followed byan upsampling operation. Operation 3304 includes generating, based onthe intermediate prediction signal, a final prediction signal. Operation3306 includes performing, based on the final prediction signal, aconversion between the current video block and a bitstreamrepresentation of the current video block.

In some embodiments for method 3300, the generating the final predictionsignal is performed by applying a Position Dependent Intra PredictionCombination (PDPC) to the intermediate prediction signal. In someembodiments for method 3300, the generating the final prediction signalis performed by generating the previously coded samples of the videowith the MIP mode and by filtering the previously coded samples withneighboring samples of the current video block.

FIG. 34 shows an example flowchart of an example method 3400 formatrix-based intra prediction. Operation 3402 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode, where the performing the conversion includesusing an interpolation filter in an upsampling process for the MIP mode,where, in the MIP mode, a matrix multiplication is applied to a firstset of samples obtained from a row and column wise averaging ofpreviously coded samples of the video, and the interpolation filter isapplied to a second set of samples obtained from the matrixmultiplication, and where interpolation filter excludes a bilinearinterpolation filter.

In some embodiments for method 3400, the interpolation filter includes a4-tap interpolation filter. In some embodiments for method 3400, amotion compensation for chroma components of the current video block isperformed using the 4-tap interpolation filter. In some embodiments formethod 3400, an angular intra-prediction of the current video block isperformed using the 4-tap interpolation filter. In some embodiments formethod 3400, the interpolation filter includes an 8-tap interpolationfilter, and a motion compensation for luma component of the currentvideo block is performed using the 8-tap interpolation filter.

FIG. 35 shows an example flowchart of an example method 3500 formatrix-based intra prediction. Operation 3502 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block according to a rule, where therule specifies a relationship between applicability of a matrix basedintra prediction (MIP) mode or a transform mode during the conversion,where the MIP mode includes determining a prediction block of thecurrent video block by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, and where the transform mode specifies use of a transformoperation for the determining the prediction block for the current videoblock.

In some embodiments for method 3500, the transform mode includes aReduced Secondary Transform (RST), a secondary transform, a rotationtransforms or a Non-Separable Secondary Transform (NSST). In someembodiments for method 3500, the rule indicates that the transformoperation using the transform mode is not to be applied in response tothe MIP mode being applied to the current video block. In someembodiments for method 3500, the rule indicates whether to apply thetransform operation using the transform mode based on a height (H) or awidth (W) of the current video block. In some embodiments for method3500, the rule indicates that the transform operation using thetransform mode is not applied to the current video block in response toW≥T1 and H≥T2. In some embodiments for method 3500, the rule indicatesthat the transform operation using the transform mode is not applied tothe current video block in response to W≤T1 and H≤T2. In someembodiments for method 3500, the rule indicates that the transformoperation using the transform mode is not applied to the current videoblock in response to W≥T1 or H≥T2. In some embodiments for method 3500,the rule indicates that the transform operation using the transform modeis not applied to the current video block in response to W≤T1 or H≤T2.In some embodiments for method 3500, where T1=32 and T2=32. In someembodiments for method 3500, the rule indicates that the transformoperation using the transform mode is not applied to the current videoblock in response to W+H≥T. In some embodiments for method 3500, therule indicates that the transform operation using the transform mode isnot applied to the current video block in response to W+H≤T. In someembodiments for method 3500, the rule indicates that the transformoperation using the transform mode is not applied to the current videoblock in response to W×H≥T. In some embodiments for method 3500, therule indicates that the transform operation using the transform mode isnot applied to the current video block in response to W×H≤T. In someembodiments for method 3500, T=256.

In some embodiments for method 3500, the rule indicates that thetransform operation using the transform mode is to be applied inresponse to the current video block being coded with MIP mode. In someembodiments for method 3500, a selection of a transform matrix or kernelfor the transform operation is based on the current video block beingcoded with the MIP mode. In some embodiments, the method 3500 furtherincludes converting the MIP mode to an intra prediction mode; andselecting a transform matrix or kernel based on the converted intraprediction mode. In some embodiments, the method 3500 further includesconverting the MIP mode to an intra prediction mode; and selecting atransform matrix or kernel based on a classification of the convertedintra prediction mode. In some embodiments for method 3500, theconverted intra prediction mode includes a planar mode.

In some embodiments for method 3500, the rule indicates that thetransform operation using the transform mode is applied to the currentvideo block when the MIP mode is disallowed from being applied to thecurrent video block. In some embodiments for method 3500, the ruleindicates that a Discrete Cosine Transform Type II (DCT-II) transformcoding technique is applied to the current video block coded using theMIP mode. In some embodiments for method 3500, the bitstreamrepresentation of the current video block excludes signaling oftransform matrix indexes for the DCT-II transform coding technique. Insome embodiments for method 3500, the performing the conversion includesderiving a transform matrix to be used by the DCT-II transform codingtechnique. In some embodiments for method 3500, the bitstreamrepresentation includes information related to the MIP mode that issignaled after an indication of a transform matrix.

In some embodiments for method 3500, the bitstream representationincludes an indication of the MIP mode for the transform matrix. In someembodiments for method 3500, the rule indicates that the bitstreamrepresentation excludes an indication of the MIP mode for pre-definedtransform matrices. In some embodiments for method 3500, the ruleindicates that the transform operation using a transform skip techniqueis applied to the current video block in response to the current videoblock being coded with the MIP mode. In some embodiments for method3500, the bitstream representation of the current video block excludessignaling of the transform skip technique when the current video blockis coded with the MIP mode. In some embodiments for method 3500, therule indicates that, for the current video block coded with the MIPmode, the MIP mode is converted to a pre-defined intra prediction modewhen the transform operation is performed by selecting a mode dependenttransform matrix or kernel. In some embodiments for method 3500, therule indicates that the transform operation using a transform skiptechnique is disallowed for the current video block that is coded withthe MIP mode. In some embodiments for method 3500, the bitstreamrepresentation excludes a signaling that indicates a usage of thetransform skip technique. In some embodiments for method 3500, the ruleindicates that the transform operation using a transform skip techniqueis allowed for the current video block that is not coded with the MIPmode. In some embodiments for method 3500, the bitstream representationexcludes a signaling that indicates using the MIP mode.

FIG. 36 shows an example flowchart of an example method 3600 formatrix-based intra prediction. Operation 3602 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode in which a prediction block of the current videoblock is determined by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, where the performing the conversion includes deriving,according to a rule, boundary samples by applying a left bit shiftoperation or a right bit shift operation on a sum of at least onereference boundary sample, and where the rule determines whether toapply the left bit shift operation or the right bit shift operation.

In some embodiments for method 3600, the rule defines that the right bitshift operation is applied in response to a number of shifted bits beinggreater than or equal to zero. In some embodiments for method 3600, therule defines that the right bit shift operation is applied using a firsttechnique in response to the number of shifted bits being greater thanzero, and where the rule defines that the right bit shift operation isapplied using a second technique in response to the number of shiftedbits being equal to zero, where the first technique is different fromthe second technique.

In some embodiments for method 3600, the boundary samples upsBdryX[x]are calculated using one of following equations: upsBdryX[x]=(Σ_(i=0)^(uDwn-1) RefX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log 2(uDwn), if uDwn>1,or upsBdryX[x]=refX[x] if uDwn=1, where uDwn is equal to a function ofthe current video block size and a boundary size, where refX [x]indicates a number of reference samples x, where >> indicates the rightbit shift operation, and where << indicates the left bit shiftoperation. In some embodiments for method 3600, the boundary samplesupsBdryX[x] are calculated using following equation:upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i]+(1<<Log 2(uDwn)>>1))>>Log2(uDwn), where uDwn is equal to a function of the current video blockand a boundary size, where refX [x] indicates a number of referencesamples x, where >> indicates the right bit shift operation, and where<< indicates the left bit shift operation.

In some embodiments for method 3600, the boundary size is predefinedbased on the current video block size. In some embodiments for method3600, uDwn is calculated as uDwn=nTbs/boundarySize, wherein nTbs andboundarySize represent the current video block size and the boundarysize, respectively. In some embodiments for method 3600, the boundarysamples upsBdryX[x] are calculated using one of following equations:upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) RefX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log2(uDwn), if nTbs>boundarySize, or upsBdryX[x]=refX[x] ifnTbs=boundarySize.

FIG. 37 shows an example flowchart of an example method 3700 formatrix-based intra prediction. Operation 3702 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block using a matrix based intraprediction (MIP) mode in which a prediction block of the current videoblock is determined by performing, on previously coded samples of thevideo, a boundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation, where the prediction samples predSamples[xHor+dX][yHor] aredetermined according to following formula in the upsampling operation:predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor,andpredSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer,where offsetHor and offsetVer are integers, where upHor is a function ofthe current video block width and a pre-defined value based on thecurrent video block size, where upVer is a function of the current videoblock height and the pre-defined value based on the current video blocksize; where dX is 1 . . . upHor−1, where dY is 1 . . . upVer−1, andwhere xHor are positions based on the upHor and yHor are positions basedon the upVer. In some embodiments for method 3700, offsetHor=upHor/2,and offsetVer=upVer/2.

FIG. 38 shows an example flowchart of an example method 3800 formatrix-based intra prediction. Operation 3802 includes generating, for aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, an intra prediction mode forthe current video block coded with a matrix based intra prediction (MIP)mode in which a prediction block of the current video block isdetermined by performing, on previously coded samples of the video, aboundary downsampling operation, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation. Operation 3804 includes determining a rule for storinginformation indicative of the intra prediction mode based on whether thecurrent video block is coded with the MIP mode. Operation 3806 includesperforming the conversion according to the rule, where the rule definesthat the bitstream representation excludes a storage of informationindicative of the MIP mode associated with the current video block.

This patent document may refer to bitstream representation to mean codedrepresentation and vice versa. From the foregoing, it will beappreciated that specific embodiments of the presently disclosedtechnology have been described herein for purposes of illustration, butthat various modifications may be made without deviating from the scopeof the invention. Accordingly, the presently disclosed technology is notlimited except as by the appended claims.

Implementations of the subject matter and the functional operationsdescribed in this patent document can be implemented in various systems,digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this specification andtheir structural equivalents, or in combinations of one or more of them.Implementations of the subject matter described in this specificationcan be implemented as one or more computer program products, i.e., oneor more modules of computer program instructions encoded on a tangibleand non-transitory computer readable medium for execution by, or tocontrol the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more of them. The term “data processing unit” or “dataprocessing apparatus” encompasses all apparatus, devices, and machinesfor processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. Theapparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of nonvolatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

It is intended that the specification, together with the drawings, beconsidered exemplary only, where exemplary means an example. As usedherein, the use of “or” is intended to include “and/or”, unless thecontext clearly indicates otherwise.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method for video processing, comprising:determining, for a conversion between a chroma block of a video and abitstream of the video, whether to apply a first prediction mode on thechroma block; generating prediction samples for the chroma block basedon the determining; and performing the conversion between the chromablock and the bitstream; wherein, in response to the determining toapply the first prediction mode on the chroma block, the predictionsamples are generated by performing a boundary down-sampling operationbased on a size of the chroma block, followed by a matrix vectormultiplication operation, and selectively followed by an up-samplingoperation; wherein the determining to apply the first chroma predictionmode on the chroma block is based on a first luma prediction mode of afirst corresponding luma block being same as the first chroma predictionmode; wherein the determining to apply the first chroma prediction modeon the chroma block is further based on a value of a syntax elementintra_chroma_pred_mode, and wherein the syntax elementintra_chroma_pred_mode relates to a mapping relation between a chromacomponent intra mode and a luma component intra mode.
 2. The method ofclaim 1, wherein in response to the determining not to apply the firstprediction mode on the chroma block, the prediction samples aregenerated by performing a luma intra prediction mode conversionoperation, followed by a chroma intra prediction mode derivationoperation, and followed by a general intra samples derivation operation.3. The method of claim 1, wherein the syntax elementintra_chroma_pred_mode specifies that a DM mode is applied on the chromablock, and wherein in the DM mode, the chroma component intra mode isidentical to the luma component intra mode.
 4. The method of claim 1,wherein the first corresponding luma block is a luma block covering aluma sample corresponding to a top-left sample of the chroma block. 5.The method of claim 2, wherein in the luma intra prediction modeconversion operation, a converted luma prediction mode is derived basedon a second luma prediction mode of a second corresponding luma block.6. The method of claim 5, wherein the second corresponding luma block isa luma block covering a luma sample corresponding to a center sample ofthe chroma block.
 7. The method of claim 5, wherein in response to thesecond luma prediction mode being same as the first chroma predictionmode, the converted luma prediction mode is derived as a normal intramode.
 8. The method of claim 7, wherein in the normal intra mode,distance-based weighted calculations are applied on reference values invertical direction and horizontal direction to generate predictionvalues.
 9. The method of claim 2, wherein in the chroma intra predictionmode derivation operation, a second chroma prediction mode is derivedfor the chroma block based on the converted luma prediction mode, andwherein the second chroma prediction mode is different from the firstchroma prediction mode.
 10. The method of claim 1, wherein in responseto a size of the chroma block being same as a size of the firstcorresponding luma block, same matrix coefficients are used in the firstchroma prediction mode and the first luma prediction mode.
 11. Themethod of claim 1, wherein the conversion includes encoding the chromablock into the bitstream.
 12. The method of claim 1, wherein theconversion includes decoding the chroma block from the bitstream.
 13. Anapparatus for processing video data comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor to:determine, for a conversion between a chroma block of a video and abitstream of the video, whether to apply a first prediction mode on thechroma block; generate prediction samples for the chroma block based onthe determine; and perform the conversion between the chroma block andthe bitstream; wherein, in response to the determine to apply the firstprediction mode on the chroma block, the prediction samples aregenerated by performing a boundary down-sampling operation based on asize of the chroma block, followed by a matrix vector multiplicationoperation, and selectively followed by an up-sampling operation; whereinthe determine to apply the first chroma prediction mode on the chromablock is based on a first luma prediction mode of a first correspondingluma block being same as the first chroma prediction mode; wherein thedetermine to apply the first chroma prediction mode on the chroma blockis further based on a value of a syntax element intra_chroma_pred_mode,and wherein the syntax element intra_chroma_pred_mode relates to amapping relation between a chroma component intra mode and a lumacomponent intra mode.
 14. The apparatus of claim 13, wherein the syntaxelement intra_chroma_pred_mode specifies that a DM mode is applied onthe chroma block, and wherein in the DM mode, the chroma component intramode is identical to the luma component intra mode.
 15. The apparatus ofclaim 13, wherein in response to the determine not to apply the firstprediction mode on the chroma block, the prediction samples aregenerated by performing a luma intra prediction mode conversionoperation, followed by a chroma intra prediction mode derivationoperation, and followed by a general intra samples derivation operation.16. The apparatus of claim 13, wherein the syntax elementintra_chroma_pred_mode specifies that a DM mode is applied on the chromablock, and wherein in the DM mode, the chroma component intra mode isidentical to the luma component intra mode.
 17. A non-transitorycomputer-readable storage medium storing instructions that cause aprocessor to: determine, for a conversion between a chroma block of avideo and a bitstream of the video, whether to apply a first predictionmode on the chroma block; generate prediction samples for the chromablock based on the determine; and perform the conversion between thechroma block and the bitstream; wherein, in response to the determine toapply the first prediction mode on the chroma block, the predictionsamples are generated by performing a boundary down-sampling operationbased on a size of the chroma block, followed by a matrix vectormultiplication operation, and selectively followed by an up-samplingoperation; wherein the determine to apply the first chroma predictionmode on the chroma block is based on a first luma prediction mode of afirst corresponding luma block being same as the first chroma predictionmode; wherein the determine to apply the first chroma prediction mode onthe chroma block is further based on a value of a syntax elementintra_chroma_pred_mode, and wherein the syntax elementintra_chroma_pred_mode relates to a mapping relation between a chromacomponent intra mode and a luma component intra mode.
 18. Thenon-transitory computer-readable storage medium of claim 17, wherein inresponse to the determine not to apply the first prediction mode on thechroma block, the prediction samples are generated by performing a lumaintra prediction mode conversion operation, followed by a chroma intraprediction mode derivation operation, and followed by a general intrasamples derivation operation.
 19. A non-transitory computer-readablerecording medium storing a bitstream of a video which is generated by amethod performed by a video processing apparatus, wherein the methodcomprises: determining whether to apply a first prediction mode on achroma block of the video; generating prediction samples for the chromablock based on the determining; and generating the bitstream based onthe prediction samples; wherein, in response to the determining to applythe first prediction mode on the chroma block, the prediction samplesare generated by performing a boundary down-sampling operation based ona size of the chroma block, followed by a matrix vector multiplicationoperation, and selectively followed by an up-sampling operation; whereinthe determining to apply the first chroma prediction mode on the chromablock is based on a first luma prediction mode of a first correspondingluma block being same as the first chroma prediction mode; wherein thedetermining to apply the first chroma prediction mode on the chromablock is further based on a value of a syntax elementintra_chroma_pred_mode, and wherein the syntax elementintra_chroma_pred_mode relates to a mapping relation between a chromacomponent intra mode and a luma component intra mode.
 20. Thenon-transitory computer-readable recording medium of claim 19, whereinin response to the determining not to apply the first prediction mode onthe chroma block, the prediction samples are generated by performing aluma intra prediction mode conversion operation, followed by a chromaintra prediction mode derivation operation, and followed by a generalintra samples derivation operation.